Dear @noris Noris!
The network itself is ok and up to date. I think it’s just about a ‘refresh-routine’:
a. After a restart of Roon or in continuous run of Roon no problems at all
b. After wake-up (I put my server to sleep-mode during night) Roon is running but does not connect the Roon-protocol-devices. This problem occurs often but not every day (strange!). My work-around: shut down roon, restart program and everything is perfect.