Changes from Web UI are not written to Samba configuration

I just added a new user to the list of account, that are allowed to access a samba share called “personal”.
According to the file /var/log/univention/management-console-module-udm.log the change has been processed:

22.04.21 13:11:20.398  MODULE      ( INFO    ) : Setting property sambaValidUsers to @personal administrator c.ruppert t.kunz
22.04.21 13:11:20.596  PROTOCOL    ( INFO    ) : Sending UMCP RESPONSE 161908988035155-515
22.04.21 13:11:20.700  PARSER      ( INFO    ) : UMCP REQUEST 161908988066351-516 parsed successfully

But when I check /etc/samba/shares.d/Personal , the user t.kunz is missing:

valid users = @personal administrator c.ruppert

I executed ucr commit but t.kunz is still missing.

How can I find out, what prevents the UCS from changing the file?

Thanks for any suggestions or hints.