Mysterious constant nozzle clogging  

Mysterious constant nozzle clogging

I've been trying to print a fairly large model about 5 times now, every time running into different problems. I created a case with Prusa support to see if they could possibly help me figure this out, but I figured it wouldn't hurt asking someone more experienced than me on here as well.

My adventure starts with the first few attempts on my MK4 printer where I got huge(1-2cm) layer shifts. After lots of debugging I tried one last time with a higher infill percentage and organic supports, which seemed to survive. The printer was past the overhangs it needs to do at the start of the print and when I woke up the next morning it was steadily printing. Then when I returned home from work I found it with a clogged nozzle, which seemed to have happened right after I left for work... That clog couldn't be fixed in any way, when I got it cleared out it would immediately clog back up causing the printer to show an error and stop printing.

So I did what everyone would do in such a scenario, and threw money against the problem. I bought the non-printable parts for the MK4S alongside a nozzle that cost me a second mortgage and a set with PPCF+PP print sheet. Then I printed the upgrade parts for the printer and upgraded my (non-mortgage)nozzle to an E3D high flow 0.4mm. I calibrated the input shaper, created new slicer settings, temperature towers and extrusion multiplier tests, and everything looked just beautiful. I printed a curling test which was perfect from the start, whereas it would curl no matter what on my MK4.

With a lot of confidence I started printing the next attempt, and now we get to the issue. The nozzle clogged. The brand new nozzle that I only did a few test prints with clogs after a few hours of printing. This time it was a full-clog without errors from the printer, causing it to print in mid air.
I followed the help pages and checked for dirty extrusion gears. Not dirty enough to cause it seizing, but OK. I pulled of the extruder and deep-cleaned the whole thing with IPA/qtips and a brass brush until all was shiny and clean again. I verified that the tension on the idler lever was ok and that the filament wasn't getting stuck in the drybox I was printing from. Oh and of course, I re-greased the parts that need to be greasy according to the manual. I also found that one bearing on the idler-lever wasn't spinning properly, so I filed away a bit until that was solved.

Next attempt, same issue. After around 4 hours of printing the nozzle starts printing in mid-air with no filament coming out. I can't remember any clicking of the extruder gears so it cannot have been very loud if there was any at all. We now know that it happens despite the extruder being in perfect condition. I also was smart enough the show the heatbreak temp in the screen. It never exeeded 36 Celsius, I constantly checked during printing. I printed with the enclosure doors open, and the temperature sensor measuring inside the enclosure didn't go above 21 Celsius. To be sure I took the roll out of the filament dryer and hung it inside the enclosure like it's meant to be.

All I can think of is maybe the extruder cover really needs to be from a different material than PPCF? Although I wouldn't know why that could matter so much, and only on long duration prints. Other than that the printed parts seems to be in really good condition. Should I print at higher temperatures to avoid this? Should I avoid high-flow nozzles altogether? You tell me, I don't know what to try anymore. Or well I could try them all of course, but I have gone from educated guesses to just guesses which isn't an effective strategy.

I tried to include the .3mf that I printed so you can see the settings, but apparently that filetype is not allowed. Weird for a 3d printing forum maybe? Anyways if you need information feel free to ask.
I printed on a modified structural profile where I put the temp on 215C, bed to 60C, gyroid infill 10%, 3 perimeters, organic supports.