Sounds somewhat similar to the issue I raised yesterday at:
Can you connect to the Roon Server manually by selecting ‘Need help finding your Roon Server?’, entering your Roon Server ip address and the selecting ‘Scan’?
This worked for me as a ‘workaround’. It is not a fix, however. On at least one occasion, the fault has recurred without provocation (I can reproduce the fault at will be clearing the Roon app data on the Android device).