Thank you for your post and we’re sorry you’re suddenly encountering a port forwarding snag.
Your diagnostic message contains a ConflictInMappingEntry line, indicating that the port Roon has attempted to assign to an automatic rule in your router via UPnP is already in use by another process or program.
Often, this is the result of a VPN or other streaming software that has reserved a range of ports. You can try changing the port listed in Roon → Settings → Roon ARC to a different number in the 50000-65000 range to start. Also check to make sure a VPN, proxy server, firewall, or other software isn’t interfering here.
Occasionally, the port mapping conflict is the result of outdated router firmware that interferes with the UPnP stack. Restart you network hardware and toggle UPnP on/off, just in case.
Lastly, certain implementations of carrier-grade NAT will trigger this error. Who is your internet service provider? It might be worth verifying that they haven’t rolled out CG-NAT to your account tier in the last few weeks.