Hey @mark_gilligan – what exactly did you change here? Have you tried disabling all firewalls completely, as a temporary troubleshooting step? Are the exceptions you put in place there for RAATServer too, or just Roon? You’ll want those configured for both.
Also, can you tell us a bit more about your Core machine and network topology, as described here?
Lastly, I know you said everything is up to date, but can you also confirm the software version of the Devialet?