[steve1977]

Thanks, I am sure your suspicion is right and it is network related. It does play SD files. I could try a locally stored file, but I am quite sure you are right and it will play as well as SD files.

The weird part is the following: I am connected wired and have not changed my network setup. It has always been working flawless, but not anymore. Not a single HD file plays well anymore. What is also weird is that I can still "cast" via UPNP from my Win10 computer to the RPi. Also, I can even play files wireless from the server on my notebook (just simple VLC play from SMB share).

Any idea what I can do to further trouble-shoot?

The server is a beefy Unraid server (see my siganture for detais).