My Roon app will no longer connect to my core.
Mike, @support should go in the body not the title. Support will need to know some things to start.
Roon remote app version and the specs of the device running it.
The specs of you Roon core machine.
The specs of your network.
That being said one of The most common causes of a sudden loss in connectivity is a change in the network or firewall or anti virus on the remote device