Why does my dampening ring keep coming loose and jamming sander?

My dampening ring keeps coming loose, which jams the sanding pad and stops the rotation. I have replaced my backing pad and rubber dampening ring, hoping it was a worn out ring, but the same problem persists. It will sometimes last a couple weeks and other times only a few seconds before coming loose and jamming the sander.

Everything else is rock-solid on this sander so I'd like to repair instead of replace.