Good evening @Ceki Gülcü

thanks a lot for your answer!,
I'm very sorry to not have added my used Logback version details. Because I immediately asked Google and found other users with the same problem, I had assumed it is a general issue.

But I am working on a project that is actually still using logback-classic version 1.2.5, so this request is obviously done.

Thanks a lot for your help solving my issue!

Kind regards,
Thomas