For anyone coming across the same issue, I found what was causing it:
For some reason if the IP address does not match in the configuration (e.g. router reboot or so) but the MAC address is correct, the LED ring will still be responsive, the ringtone playing will not.
Are you 100% sure this is the reason? I have a DHCP reservation made, still my system is unable to play any sounds through the hub, while in the past this had worked just well.
I could fix the issue twice by updating to the new IP address. Don’t know if there are other issues, but at least that one got it fixed for me. Try changing the IP lease to another IP and updating your config (and power cycle your hub of course).