After updating the Core this morning on my headless server, all connections from PC and phone fail. System was previously working. Have updated PC and phone software with no success.
I fixed my similar symptom – if your Roon Core and Clients are on different VLANS, you need to enable firewall ports TCP 9332 and 9330 from the Client to Core VLAN.
You may also have to update any Windows firewall rules, or on Lunux if you’re using UFW or other firewall.
Looks like Roon changed what was working (access port TCP 9003) to TCP 9332 & 9330.
Noted, above, depending on what OS you’re running Roon Core on, you may need to update Windows Firewall or Linux UFW to enable traffic to ports 9332 (minimum) & seemingly to 9330 as well.
Try turning off any anti-virus programs on your core machine temporarily to see if the problem goes away. If it does, add Roon to the list of exceptions.