Yesterday before leaving work, I left a bunch of parts to print on our Prusa Mk4. This morning, I found all the parts with the same defect at the bottom: apparently the magnetic printing plate shifted ⅛¨ sideways on the bed 3 or 4 layers into the 7-hour print.
Unfortunately, I removed the magnetic plate without paying attention before I saw the defect, so I'm not really sure if this is what happened. It stands to reason, but it might also be both stepper motors somehow skipping at the same time. It seems unlikely, but maybe there has been a power brownout or something.
Or someone at the office interfered with the bed's movement at some point. But it seems unlikely too.
If the plate itself shifted, maybe it's because I had cleaned it with water just before and I may have left some slightly damp spots underneath, despite drying it as good as I could. I might also have failed to position the plate against the registration pins at the back of the bed, but I usually pay attention so that too is unlikely. Still, I might have been careless.
Has anybody had this sort of thing happen before? This is the first time for me.
The idler is gripping the filament just fine. I know that because I have to loosen it when I print really soft TPE and I tighten it back up and readjust the idler pressure when I print PLA or PETG - and I did that a few days ago.
The belts might be getting loose though. I haven't checked them. They look tight but the printer has a lot of mileage, so I guess it's worth checkout out. But the re-print I just did of the same bgcode just completed fine.