Problem: Erros in log.smbd
Even though all appears to be running find you notice messages as the following in
Error loading module '/usr/lib/x86_64-linux-gnu/samba/vfs/acl_xattr.so': /usr/lib/x86_64-linux-gnu/samba/libreplace.so.0: version `SAMBA_4.10.0RC2_UNIVENTION' not found (required by /usr/lib/x86_64-linux-gnu/samba/vfs/acl_xattr.so)
This started right after performing a successful update of your Univention UCS. A restart of samba does not help.
This happens because of some updated libraries which use kernel functions. In order to solve you need to reboot your server so the new libraries get loaded by the kernel.