I have a Prusa3D i3m3s. The problem occurred once before with firmware 3.6.1. Last night I upgraded to firmware 3.7.1 and repeated the problem almost exactly.
The symptom is that at what appears to be the same point in the print in the two failure instances, the extruder stops extruding. There are a few wisps of filament on both failures. The print continues to completing. At the end of the print, the firmware issues an error because the MMU2s can not properly retract the filament.
On analysis, the filament is tightly jammed into the extruder and hot end, almost as if there has been heat creep. Slow, strong, and steady tension on the filament will withdraw it from the extruder system.
The hot end heats normally, and maintains temperature. When hot, plastic extrudes properly from the hot nozzle.
The thermister wires are damaged from an earlier problem.
The damage points to a thermister-related problem, but a shorted or open thermister is easy to detect in firmware. I would expect it to throw an error and stop the print.
My question is: Does the Prusa3D firmware detect open/shorted thermisters and stop the print?
If a photo is required, I can post that tomorrow.