Modified PRUSA adapter-printer-mmu2s part.
This part guides the filament from the PTFE tube to the gears in the extruder. IMHO the inlet of the part is too small/steep (see image right). This causes filament to stuck before the gears. This behavior becomes more pronaunced if the curvature of the filament increases when the roll is emtying.
Therefore I modified the guiding hole to be a cone and increased the inlet diameter to 3.5 mm (see image left).