Playback music directly from Media Server folders?

Hi all,

I try volumio (Raspi 3, Version 2.698) as a substitute for my old but beloved noxon 2 audio. I am very satisfied with most of its features along my trial…
Question: Connection to my NAS via cifs with credentials works fine! If I click on the browse tab and try to access media server by clicking the icon, I can see all relevant content. If I click on browse “by folder” I see all files and subsequent sub-folders. Any attempt to play one music file directly does not work, but if I click into a sub-folder, a play icon appears (top right side). A click on that one plays all the files just fine.
BUT: again a click on any file within this sub-folder to play directly or by choosing the 3-dots on the right hand side and click play, add to queue or add to playlist…) does not work.

What’s the problem here?
Thanks for any hint!