I'm not even sure exactly what's going wrong, but it appears that BDS 1.16.100.4 on Ubuntu 20.04 LTS with all the latest updates keeps losing the connections to any clients.  The BDS console doesn't show any disconnection, and the client appears to keep working, but you can't access the inventory and no changes made to the world are permanent.  Restarting BDS and reconnecting fixes it...for a little while.  Then it recurs.

I don't know what further info I can give since there are no logs I can find.