Bugs & Errors - Prusa3D Forum

upload to Printer

Rastafly — Mon, 15 Jun 2026 19:47:12 +0000

Uploading to the printer always takes several minutes, and sometimes nothing happens at all even though the printer is ready. What can be done about this?

MMU3 filament manipulation operations REALLY need a cancel button

dementeddr — Thu, 28 May 2026 02:48:13 +0000

Printer: Core ONE

Printer Firmware: 6.5.3+12780

MMU3 Firmware: 3.0.4

Sometimes when I try to load filament into the MM3, things don't quite line up correctly. Sometimes the filament can't quite bridge the gap from tube to tube over the pulley gears in the right spot. Most commonly, the filament tip is bent and it misses the hole to the selector gets pushed out of the MMU entirely. I've also had it just catch on the hole to the selector and get ground away between the pulley gear and idler. Either way, the filament does not reach the sensor in the selector and so the pulley just keeps running and running and there is no button on the screen to stop it. I've had to pull out the PTFE tube from the selector and shove a piece of filament in to trigger the sensor. That works okay if I'm just loading new filament to the MMU, but I've had it happen in the middle of multi-material prints too and failed to get everything back in place before the MMU tried advancing the next filament, which forced me to scuttle the print.

Once I had an issue retracting a filament from the print head to the MMU, where it jammed in the extruder gear. The pulley gear just kept grinding it away until it broke while I scrambled to get it unjammed.

I also had an intermittent issue for a long time that was caused by a poorly calibrated filament sensor on the MMU (my fault), which would occasionally cause the MMU to think it had finished retracting a filament when it had not, and then try to move the selector with filament still in it. That was a huge pain to clean up, in part because when I tried to retry retracting the filament, the selector carriage would try to re-home first while filament was still stuck in it.

The point is, sometimes shit happens. Right now, there is no software contingency for dealing with it. When the MMU is loading or unloading or switching filament (even when it's a user-initiated operation and not part of a print), there's no way to just tell it to stop from the printer screen. There's no button to cancel the operation, or to go back to the home screen so you can go to the Control menu and disable the motors. You have to do dumb hacky things like pull out PTFE tubes and jam filament into sensors, and then do more dumb hacky things to clean up the situation afterward. Or hit the reset button and kill whatever you were trying to accomplish at the time.

Please please please please please add cancel buttons to at least the MMU filament loading and unloading screens. Preferably they would be added to any MMU operation screen that doesn't have them. I don't know what kind of complexity that means adding to the state machine behind those operations. Maybe there isn't a good recovery path once the operation is paused in an unknown state. But something is still better than nothing.

MMU3 can't be enabled for Core ONE unless side filament sensor has been calibrated, even though it isn't needed.

dementeddr — Thu, 28 May 2026 02:11:30 +0000

Printer: Core ONE

Firmware: 6.5.3+12780

I was recently printing with a filament that doesn't work well with the MMU3, so I had it disabled and was feeding filament in through the side input. When I was preparing to switch back to using the MMU, something got jammed in the side filament sensor, and it was stuck reporting that there was filament present when there wasn't. I tried to recalibrate the sensors, but it failed. I decided to switch back to using the MMU again at that point, but I couldn't re-enable it in the printer settings because the filament sensor calibration had failed. I ended up having to take off the side panel and disassemble the side filament sensor to clear the jam before I could run a successful calibration and finally re-enable the MMU.

To reiterate, I could not enable the MMU in the printer settings because the side filament sensor calibration had failed, even though the fact that I am using the MMU means that I don't need the side filament sensor at all. I had to partially disassemble the printer to fix a hardware problem completely unrelated to the MMU before I could use the MMU.

I'm assuming the calibration check is in place because it's risky to run the MMU3 when the toolhead filament sensor is not reporting accurately. I'm also assuming the calibration check is just checking the result of the Filament Sensors step of the Calibrations and Tests menu as a whole, and failing one of them them fails the whole thing. That would mean the two sensors need to be calibrated separately. Although now that I say that, I'm not sure what calibration actually needs to happen for the side filament sensor. It seems to be pretty binary, unlike the toolhead sensor. Maybe it doesn't need to be checked at all?

Files won't download to printer

cmpickle — Sun, 03 May 2026 19:55:27 +0000

I ran into an issue where I had my printer in a ready state and a file in the queue but the file just said "not downloaded to printer". I tried a bunch of things and uploading the file more times. It turned out that the problem was I had at one point uploaded a file a few times in succession that had the same name. This was because the prusa slicer uses the name of the project and so some files were named the same thing that weren't intended to. This was causing the error "file with that name already exists on the printer" on the dashboard view. I didn't notice that there for a long time as I was looking at the queue and files tab. I eventually found that and deleted those file transfers that had the same name and my files transferred correctly again. I think the printer shouldn't get stuck if you try to transfer files of the same name. It could append a unique identified like if you copy pasted a file with the same name would do or it could at least just fail the transfer outright without clogging up the file transfer queue. As it is it's a terrible user experience and was not at all obvious on what I needed to do to get files transferring again.

Old Removed Printers Cause Error message upon login when they are not found.

bryn51 — Tue, 21 Apr 2026 00:17:27 +0000

I once had 4 printers, but sold two of them. I removed them from prusa connect. But ever since that day, when I log in (web) to Prusa Connect, it comes up with several error popups "Error Printer not found or does not belong to the given user".

Clearly Prusa Connect hasn't got the memo about those printers and still thinks I have them, tries to find them in my list of current printers but faiis. I searched everywhere for a reference to those old printers to amend the list, but nothing. Seems clear that there is an error of logic in the opening screen code somewhere. Or a missing page that would allow the user to see and amend the list of affiliated printers with the current login. Or perhaps a deficiency that occurs when a printer is removed, not completely removing all related data. I'm just guessing.

Whatever is the cause I suggest that its annoying to users, and ought to get some attention.

"Printing time" is really "time on this tab"

André — Sat, 18 Apr 2026 11:27:41 +0000

This time is "how long you watch this tab,"

(you need to click the screenshots, this forum does a lousy job.)

switch to any other, like "print history" , and back:

if you open this well into a print, and see printing time <1m ... you know something is wrong.

Slicer crashes 100% of the time at Connect login

vtgearhead — Sun, 12 Apr 2026 16:35:15 +0000

Title says it. Under Ubuntu Linux 24.04 I see a dialog box referencing some new authentication scheme, followed by an immediate crash. 100% repeatable. Works on a Mac Mini running Sequoia, FWIW. Whatever new security layer this might be it doesn't play nicely.

P0: Slicer unuseable: 2026-04-10 11:50 am - Slicer broken, cors error

killakatze — Fri, 10 Apr 2026 09:54:04 +0000

Please fix the cors error, the slicer is 100% unuseable

manifest.webmanifest:1  Failed to load resource: the server responded with a status of 403 ()Understand this error
slice:1 Manifest fetch from https://www.printables.com/manifest.webmanifest failed, code 403Understand this error
manifest.webmanifest:1  Failed to load resource: the server responded with a status of 403 ()Understand this error
slice:1 Manifest fetch from https://www.printables.com/manifest.webmanifest failed, code 403Understand this error
 📤 External app message 
3 📩 External app event 
 Setting token to expire in 5197245.697975159 ms
 📩 External app event 
 Setting token to expire in 5197192.698001862 ms
pagead2.googlesyndication.com/ccm/collect?rcb=3&frm=0&ae=g&en=page_view&dl=https%3A%2F%2Fwww.printables.com%2Fslice&scrsrc=www.googletagmanager.com&rnd=970452239.1775814471&navt=r&npa=1&ep.ads_data_redaction=0&gdid=dY2Q2ZW&_tu=CA>m=45He6490h2v811757514za200zd811757514xea&gcs=G100&gcd=13q3q3q2q5l1&dma_cps=-&dma=1&tag_exp=0~115938465~115938468~117384405~118131808&apve=1&apvf=f&apvc=1&tft=1775814471065&tfd=1238:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
pagead2.googlesyndication.com/ccm/collect?rcb=3&frm=0&ae=g&en=page_view&dl=https%3A%2F%2Fwww.printables.com%2Fslice&scrsrc=www.googletagmanager.com&rnd=970452239.1775814471&navt=r&npa=1&ep.ads_data_redaction=0&gdid=dY2Q2ZW&_tu=CA>m=45He6490h2v811757514za200zd811757514xea&gcs=G100&gcd=13q3q3q2q5l1&dma_cps=-&dma=1&tag_exp=0~115938465~115938468~117384405~118131808&apve=1&apvf=f&apvc=1&tft=1775814471065&tfd=1238:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
region1.google-analytics.com/g/collect?v=2&tid=G-3HK7B7RT5V>m=45je6490h2v874122347z8811757514za20gzb811757514zd811757514&_p=1775814470970&gcs=G100&gcd=13q3qPq2q5l1&npa=1&dma_cps=-&dma=1&gdid=dY2Q2ZW&_eu=EAAAAGA&are=1&cid=23495164.1775814471&frm=0&ir=1&pscdl=denied&rcb=5&sr=1512x982&uaa=arm&uab=64&uafvl=Not%253AA-Brand%3B99.0.0.0%7CGoogle%2520Chrome%3B145.0.7632.110%7CChromium%3B145.0.7632.110&uam=&uamb=0&uap=macOS&uapv=15.7.4&uaw=0&ul=en-gb&_s=1&tag_exp=0~115938465~115938468~118442252&sid=1775814471&sct=1&seg=0&dl=https%3A%2F%2Fwww.printables.com%2Fslice&dt=EasyPrint%20%7C%20Printables.com&_tu=CA&en=page_view&_fv=1&_nsi=1&_ss=1&ep.event_name=page_view&tfd=1291:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
region1.google-analytics.com/g/collect?v=2&tid=G-65PWSTXL4S>m=45je6490h2v871191087z8811757514za20gzb811757514zd811757514&_p=1775814470970&gcs=G100&gcd=13q3qPq2q5l1&npa=1&dma_cps=-&dma=1&gdid=dY2Q2ZW&_eu=EAAAAGA&are=1&cid=23495164.1775814471&frm=0&ir=1&pscdl=denied&rcb=9&sr=1512x982&uaa=arm&uab=64&uafvl=Not%253AA-Brand%3B99.0.0.0%7CGoogle%2520Chrome%3B145.0.7632.110%7CChromium%3B145.0.7632.110&uam=&uamb=0&uap=macOS&uapv=15.7.4&uaw=0&ul=en-gb&_s=1&tag_exp=0~115938465~115938469~117266401~118131808&sid=1775814471&sct=1&seg=0&dl=https%3A%2F%2Fwww.printables.com%2Fslice&dt=EasyPrint%20%7C%20Printables.com&_tu=SA&en=page_view&_fv=1&_ss=1&ep.event_name=page_view&tfd=1310:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
pagead2.googlesyndication.com/ccm/collect?rcb=17&frm=0&ae=g&dl=https%3A%2F%2Fwww.printables.com%2Fslice&scrsrc=www.googletagmanager.com&rnd=970452239.1775814471&navt=r&npa=1&ep.ads_data_redaction=0&did=dY2Q2ZW&gdid=dY2Q2ZW&_tu=CA>m=45be6490h2v9116191347z8811757514za20gzb811757514zd811757514xea&gcs=G100&gcd=13q3qPq2q5l1&dma_cps=-&dma=1&tag_exp=0~115938465~115938469~117384406&apve=1&apvf=f&apvc=0&tids=AW-958555779&tid=AW-958555779&tft=1775814471195&tfd=1369:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
 Guest data expired, not restoring printers/projects
pagead2.googlesyndication.com/ccm/collect?rcb=17&frm=0&ae=g&dl=https%3A%2F%2Fwww.printables.com%2Fslice&scrsrc=www.googletagmanager.com&rnd=970452239.1775814471&navt=r&npa=1&ep.ads_data_redaction=0&did=dY2Q2ZW&gdid=dY2Q2ZW&_tu=CA>m=45be6490h2v9116191347z8811757514za20gzb811757514zd811757514xea&gcs=G100&gcd=13q3qPq2q5l1&dma_cps=-&dma=1&tag_exp=0~115938465~115938469~117384406&apve=1&apvf=f&apvc=0&tids=AW-958555779&tid=AW-958555779&tft=1775814471195&tfd=1369:1  Failed to load resource: net::ERR_BLOCKED_BY_CLIENTUnderstand this error
 Guest data expired, not restoring printers/projects
 AccountId 311493 sid='TV93_TR6r_5reNrUAb5f' joined their user room
249The resource  was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it has an appropriate `as` value and it is preloaded intentionally.Understand this warning
 EasyPrint Extension not detected
(anonymous) @ app.BjQHjwPD.js:13
(anonymous) @ Bom16hJ5.js:23
r @ app.BjQHjwPD.js:483Understand this warning
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/files/?page_size=30' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/files/?page_size=30:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:734 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/files/?page_size=30&used=0' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/files/?page_size=30&used=0:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:734 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/files/?page_size=30' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/files/?page_size=30:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:734 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/file/' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/file/:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:512 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
 📤 External app message 
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/project/' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/project/:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
2 📤 External app message 
Bom16hJ5.js:682 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1  GL_INVALID_OPERATION: glTexStorage2D: Texture is immutable.Understand this warning
5Bom16hJ5.js:682 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/projects/?page_size=20&search=&user_deleted=0' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/projects/?page_size=20&search=&user_deleted=0:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:734 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/projects/?page_size=20&search=&user_deleted=1' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/projects/?page_size=20&search=&user_deleted=1:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
slicer.printables.com/app?lang=en&theme=auto:1 Access to fetch at 'https://slicer-api.printables.com/api/profile/' from origin 'https://slicer.printables.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.Understand this error
slicer-api.printables.com/api/profile/:1  Failed to load resource: net::ERR_FAILEDUnderstand this error
Bom16hJ5.js:24 Uncaught (in promise) TypeError: Failed to fetch (slicer-api.printables.com)Understand this error
sentry.prusax.com/api/39/envelope/?sentry_version=7&sentry_key=c38a1591365aca6b5e335c6ac5f6286c&sentry_client=sentry.javascript.sveltekit%2F9.17.0:1  Failed to load resource: the server responded with a status of 400 ()Understand this error
app.2.BjasK4u4.js:5

Prusa Connect Preferences - Stated "Feedback form" doesn't exist

UjinDesign — Mon, 23 Mar 2026 18:26:10 +0000

Hi.

I just noticed that there is a new "Preferences" section on the Prusa Connect website. Here, there is a notice saying that feedback through the feedback form. See image. However... there is no feedback form? Or at least I cannot find it.

80906767-screenshot-from-2026-03-23-19-23-22.png

Time to sort Connect?

Mike01Hu — Thu, 19 Mar 2026 18:55:51 +0000

Prusa Connect is a pain if you stop a print via the PC and always has been with MK3/4/Core 1. It's clumsy in the way it handles the command and when deleting files in the printer, queue or wherever, requiring multiple digging through the tabs to get any sense, understanding strange warnings and often requiring attending the printer to kick it back into a sensible mode. Don't get me wrong, I like it and use it all the time, but stopping a print using Connect is always done with trepidation!

Common guys, let's see some action here, too!!!