I replaced the Aris XB6 router with a Unifi Security Gateway and AP AC Lite 3 months ago and I can confirm all issues have been resolved comprehensively. It appears as though the router couldn’t maintain the sessions (even though the connections didn’t actually drop) for whatever reason. Perhaps the ISP-provided routers aren’t as good as they think they are.
Apologies to the Roon team for blaming them for a network issue.