I don’t have a Linn device, so this might not be constructive, but I wonder if there is some configuration that needs to take place. In Settings/Setup there is a field called Linn Streaming Subnet, with an IP address. See this link where that fixed the issue for someone else:
Additionally the Linn page on the Roon site suggests ensuring your firmware on the Linn device is up to date. Perhaps you need to update that?