Hi @Noris,
that was the clue - yes, this CentOS server also has an Emby server running on it, which has DLNA enabled (ie. it was using port 1900.)
Stopping Emby (in this case in the form of Jellyfin) and re-starting Roonserver took care of the Roon issue.
I didn’t know Roonserver used DLNA. Is it possible to either disable DLNA in Roon, as I do not want to connect to the music library from any DLNA clients, or if DLNA is required for the Roon client communication to work, can Roon and its remotes / endpoints be told to use a different port? Possibly it’s not specifically DLNA but the SSDP protocol…
Sincerely
Chris