Odd that one motor goes unstable with Ap = 200 or so while the others manage 1000 or so. Perhaps you could swap a couple of them over to see if the problem stays with the motor.

Unless you are shifting a massive (large mass and / or large force) load on one of them, they shouldn't be significantly different. Have you got similar encoder PPRs in the drive and similar steps per pulse in the controller? It's possible that could change the system gain enough to cause this issue - not sure how that would work without actually thinking it through.

There are also a few parameters in there that I don't recall or understand immediately. At the very least you should ensure they are consistent for all the drives if you want to eliminate this strange behaviour. Perhaps a parameter reset would help.