FMPro layout mode lockup has been persistent since 20, and remained in 21
The other items are less prevalent, but are widely reported.
There is also the issue that after a deployment, a privilege set is commonly screwed up, and has to be rebuilt.
Also not a bug, per se, but the order of execution of user accounts in Linux has been reported to be alphabetical, not listed order (not tested so hearsay).
There has been a couple more serious bugs in 21 on Linux and Mac, that have caused some of the major FM shops to revert clients to 20 (although same bug reported on 20.3.1 as well), but I've not experienced those issues. The one on large scale data loss is a biggie. Claris has not yet been able to replicate AFAIK
Thanks @Kirk - crashes and other misbehaviors I can live with, but data corruption issues seem scary. I think I'll stay with my current versions for now and hope FM gets those critical issues fixed (or comes up with setting that prevent it from happening).