SOLVED: Playback error - Unable to find a valid media source to play

[dalben]

Hmm, this is a pretty odd issue.

The fact that the stream URL does work leads me to think this is a web client issue. Have you tried a non-web client like Swiftfin, Android TV, etc to see if the files play there?

Sounds like a bug with your shows library prevents the web client from being able to play it for some reason.

I tried with Swiftfin and it worked quite smoothly

Same here.  Swiftfin worked.  The webclient struggles as does the Android client.  Also noticed that when using Kodi, the library misses seasons or all the shows.  Re-identifying the shows seems to correct the issue.  Reconfirming that adding a show to the playlist and playing from the playlist works fine.