Ceph Dashboard suddenly fails - Port not free?

[petwri]

I have had my ceph dashboard running for quite some time, but now ceph is suddenly complaining that the port is not free.

    health: HEALTH_ERR
            Module 'dashboard' has failed: Timeout('Port 8080 not free on 10.0.0.103.')

Some info on the dashboard setup:

root@node03:~# ceph config get mgr mgr/dashboard/server_addr
10.0.0.103
root@node03:~# ceph config get mgr mgr/dashboard/server_port
8080

But 8080 is only open for ceph:

root@node03:~# ss -tulnp | grep :8080
tcp   LISTEN 0      5         10.0.0.103:8080      0.0.0.0:*    users:(("ceph-mgr",pid=2350224,fd=22))

After ceph mgr module disable dashboard, the port is not used. It looks as if the dashboard is locking itself out. Any ideas?