I've had the same issues on two fresh installs of Unraid 6.90r2 & also running it on a Ubuntu instance.
usermod: no changes
2020-12-24 13:13:28,734 CRIT Set uid to user 0
2020-12-24 13:13:28,740 INFO supervisord started with pid 13
2020-12-24 13:13:29,744 INFO spawned: 'dbus' with pid 16
2020-12-24 13:13:29,747 INFO spawned: 'avahi-daemon' with pid 17
2020-12-24 13:13:29,749 INFO spawned: 'squeezeboxserver' with pid 18
2020-12-24 13:13:29,775 INFO exited: avahi-daemon (exit status 255; not expected)
2020-12-24 13:13:30,777 INFO success: dbus entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2020-12-24 13:13:30,778 INFO spawned: 'avahi-daemon' with pid 19
2020-12-24 13:13:30,778 INFO success: squeezeboxserver entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2020-12-24 13:13:31,059 INFO exited: squeezeboxserver (exit status 0; expected)
2020-12-24 13:13:32,061 INFO success: avahi-daemon entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2020-12-24 13:13:32,064 INFO spawned: 'squeezeboxserver' with pid 22
2020-12-24 13:13:32,959 INFO exited: squeezeboxserver (exit status 0; not expected)
2020-12-24 13:13:33,964 INFO spawned: 'squeezeboxserver' with pid 25
2020-12-24 13:13:34,820 INFO exited: squeezeboxserver (exit status 0; not expected)
2020-12-24 13:13:36,827 INFO spawned: 'squeezeboxserver' with pid 28
2020-12-24 13:13:37,701 INFO exited: squeezeboxserver (exit status 0; not expected)
2020-12-24 13:13:40,709 INFO spawned: 'squeezeboxserver' with pid 31
2020-12-24 13:13:41,591 INFO exited: squeezeboxserver (exit status 0; not expected)
2020-12-24 13:13:42,592 INFO gave up: squeezeboxserver entered FATAL state, too many start retries too quickly