Comment 7 for bug 1755383

The logs really have no info about what happened on upgrade.

But if that is reproducible you should be able to run e.g.
  $ sudo apt install --reinstall samba

That should trigger the error again and after that the logs should hold some info why they failed to start.

TL;DR:
1. $ sudo apt install --reinstall samba
2. If above fails report the content of the two logs after that
3. sharing the full output of
   $ systemctl status smbd
   $ systemctl status nmbd