Only plays when locked in

This is not only a remote issue, I guess.
I have installed the new version of Audirvana on my mac mini with macOS 10.13.6.
I use iOS and iPad OS 13.2.2.
Once in a while, Remote does not find the server. This is not a network issue because I can vnc into my mini. Just the Audirvana server does not seem to respond.
But even worse:
I lock into the min using VNC ans start Audirvana and it plays. I leave it alone, the song ends, nothing else plays.
I open the VNC connection, the music continues to play. The sond finished, I dont use VNC, it stops. I open the VNC window, the music continues.
This feels weird. And I dont know of there is a new setting I have to select such as: Only play music when a remote connection via VNC is made, or such.
So being on a Mac, if I want to constantly listen to music, I have to keep a VNC window open. My mini never goes to sleep and wake up on WLAN is activated. What else can I do?