Is your Roon Server an earlier build than version 2.60? If so, then your issue is being caused by an incompatibility between Roon clients version 2.60 and earlier versions of Roon Server. See:
Roon Bridge 2.60 (build 1501) Production with EA Roon Server - Early Access - Roon Labs Community
Either update your Roon Server to version 2.60 (Production) or, if you are running Early Access builds of Roon Server, wait until Roon Labs release a new Early Access version.