XL Loose Belt Retainers
Check your belt retainer screws!
This is just an FYI. I had been having seemingly random homing errors. I started with checking belt tension, using the both the belt tuner app and by checking the carriage against the front of the frame. I could never get the tension perfect on both sides, 1 was a little loose and the other to tight. They were both close so I let it go.
I continued to have weird homing errors and random crashes. During one of the crashes the belt retainer cover got some scuffing on it so I decided to reprint it.
Low and behold when I took the cover off all of the screws on both belt retainers were loose and once the cover was off the upper belt fell out of the retainer.
I have never taken this apart so it had to have come this way from Prusa, or they worked themselves loose form heating and cooling cycles.
So I added some thread locker and put it back together. When I tensioned the belts this time I easily got both sides perfect.
So next time your doing maintenance it might be for to make sure the screws on your belt retainer are tight.