I'm having this problem. What is the idler arm you mentioned? I had to take everything apart and I can see (as shown in the attached picture) where the filament is stuck
I've got the 1.5XT+ and this has happened when the heated bed cord gets snagged and yanks on the bed. I also have a lot of problems with the printed part that holds the BLTouch sensor and am constantly reattaching it. It will cause this problem if the BLTouch gets lose and snagged on a print...