1. I pulled all filament out of the MMU3 and the filament buffer manually.
2. I loaded new filament into slots 1 through 4 by following the "Preload to MMU" prompts.
3. I used the "Cut filament" prompt to check that filament 1 was properly loaded. I did this because the loose filament in the buffer repeatedly got caught on something as I put the cartridge back into the buffer.
4. I hit the reset button because the MMU3 got caught in a loop trying to cut filament 1, indicating that the filament had become partially unloaded (as I had expected).

Since then the MMU3 has been completely nonfunctional. When powering on, it does not attempt to home at all. There are no motor noises of any kind. The filament selector stays on filament slot 1, and the LED for slot 1 is lit green. The filament selector buttons yield no response. The MMU3 reset button causes the unit to flash lights as if rebooting, but then it goes back to the same state: stuck on filament slot 1 with the slot 1 LED lit green. At no point does the Core One's LCD screen indicate that an error has occurred.

I have taken the following steps to troubleshoot / resolve the problem:

• I have verified that the FINDA sensor is not detecting any stray filament by inserting a small piece of filament into the sensor. When I insert the filament, the red LED on the FINDA turns off. When I remove the filament, it turns on. There are no other changes to the MMU's state.
• I have re-flashed the MMU3 with the latest firmware. PrusaSlicer indicated that the firmware flash was successful. However, upon rebooting, the MMU3 returned to that same state: stuck on filament slot 1 with the slot 1 LED lit green.

I am inclined to think that the filament selector motor has failed, but I want to rule out other possibilities before I contact support for a warranty replacement. What other troubleshooting attempts should I take?

Right after booting the printer, the MMU starts moving and produces a loud rattling noise for about one second. It sounds like the idler is trying to find its position. After that, the unit seems ready and no error messages are shown.

I did some research but couldn’t find any videos or examples where the MMU behaves like this. In other setups, the idler appears to move smoothly to its end positions without noticeable noise.

I already checked the following:

1. The idler drum rotates freely
2. The small gap to one side (as described in the assembly instructions) is present
3. The idler is firmly mounted on the shaft
4. on both the MMU and printer is up to date
5. No error messages are displayed

Despite all of this, the rattling noise during initialization remains.

Has anyone experienced similar behavior or has an idea what might be causing this?

THANK YOU SO MUCH

The same happens when I load the filament to the nozzle. This is working because I have selected the "standard nextruder". But unloading does not work.
Is there some configuration I need to modify?

I've just updated to the "new" firmware, and on my first print I had the layers shift.  This happened three times.  The culprit is the wipe tower.  For some reason, large blobs of filament are deposited into the wipe tower on filament change.  Eventually, the buildup will cause the extruder to drag and the motors will skip steps.

This is happening on my CoreOne+.  I've got the Coreboxx on top with active smart rewinders by @mire.

I've tried adjusting settings on the wipe tower, and it makes no difference.  Eventually the extruder crashes and ruins the print.  I've tried this print three times now.