Problem with filament loading on MMU 2.0s. Only 3/5 filaments can load two others are blocked by the selector.  

RE: Problem with filament loading on MMU 2.0s. Only 3/5 filaments can load two others are blocked by the selector.

I had a similar problem. My filament paths and tips looked good visually, but
Filament 4 just didn't want to load, and test prints with Filament 2 worked perfectly, but when
testing the loading it sometimes just didn't want to load.

My problem was probably the tips. It was a new cut tip, but most likely the
filament was bending a bit, so it managed to catch an edge somewhere.
Feeding the buffer also put some stress on the filament - so it was likely to bend.

Some things to do:

Check for simple mechanical errors first:
- check filament path for blocking objects
- check printed parts for small print-errors that need correction
- check filament tips
- check tubes (maybe a screw is holding the tube too tight)

After that maybe some mods could help:
1) Replacing the screws that hold the tubes with pneumatic fittings.
This could avoid a screws squeezing the tube, and could make it easier to check/change things.

I found those for MMU2s and the buffer:
https://www.thingiverse.com/thing:3233579
https://www.thingiverse.com/thing:3545935

2) Maybe cutting the tips differently could help.
Maybe there's something like a pencil sharpener that fits for filament.

3) Maybe this mod can make the Selector more forgiving to bad tips:
https://www.prusaprinters.org/prints/1829-prusa-mmu2-refined-selector

I also wonder whether chamfering the tubes on both ends might help loading.
But my guess is that all this would probably just move the problem
down to the extruder, where problems would be a lot worse.