Presuming you had no issues during printing, the hot end not being up to temp is the most likely reason.
I recently had a print fail (at home) with the extruder skipping. Hot end was reporting to temperature, attempting to unload, the extruder could not pull it out of the hot end. I eventually did manage to pull it out. I cut a few inches off and loaded it back up with no further extrusion problems. I was using clear PETG, and did not see any foreign objects in the pulled end. All I have guessed is that maybe the filament had a pellet of foreign plastic in the extruder feed, with a higher melt point that didn’t melt through the hot end.