Are you able to downgrade to version 2:4.15.13+dfsg-0ubuntu1.2 and verify that the problem is not present with that version? This will help understanding if you are actually hitting a regression in the samba package.
Downgrading is not straightforward, but you should be able to do it by doing something like:
Hello Somogyi and thanks for this bug report.
Are you able to downgrade to version 2:4.15. 13+dfsg- 0ubuntu1. 2 and verify that the problem is not present with that version? This will help understanding if you are actually hitting a regression in the samba package.
Downgrading is not straightforward, but you should be able to do it by doing something like:
$ apt install --no-install- recommends ubuntu-dev-tools dfsg-0ubuntu1. 2
$ pull-lp-debs samba 4.15.13+
$ apt install ./*.deb
Note that this is likely to install some packages you didn't have installed before, and in general it is not a best practice.
Thanks!