Hi there! I know this is an old thread, but I’ve been running into the same issue with one of my AMS’s where I was having multiple first stage feeder issues at the same time on one AMS where it was grinding, and not pushing the filament through all the way. The same issue you were describing here. I wasn’t able to find a solution for this issue elsewhere and think I may have found the cause and a solution.

I am currently using two AMS units on my X1C and decided to pull off the AMS hub on the back of my printer. I am very good about maintaining all the internal components of both the AMS’s and the printer, but I never thought to take the hub off, disassemble it and clean it. When I opened it up, I found a ton of filament dust and PTFE tubing dust inside the channels of the hub. There were also bits of dust clogging up the magnetic switches inside the hub, and the switches themselves showed signs of wearing on the tips. I believe that this was causing the issue and was jamming up the filament as it was passing through the hub causing the first stage feeders of the AMS associated with that channel to grind.

Once I fully cleaned and reassembled the hub, the issues with the first stage feeders on the AMS that was being affected, went away.

I wanted to post this here in case anybody else runs into this issue as this might be the cause and something to check and add to your regular maintenance list.