Zerotier not connecting to central (Raspberry in bridge mode)

I have setup a Respberry PI with zerotier 1.12.2 behind a firewall; Zerotier is configured on bridge mode… Firewall allows all outbound traffic from zerotier IP. Zerotier initially registered (and was authorized) on Zerotier central.
Nevertheless the status is OFFLINE and all planets are in RELAY mode.
I left it some days and then it went ONLINE and traffic was flowing. Then i rebooted the Raspberry and it went again offline with no connections appearing in netstat -an.

After some hours, it is still offline, but netstat -an shows many connections to (seems fallback mode, but it is not working). After some other hours, it started working again in fallback mode TCP and after some minutes it went back to offline (I did not touch anything both on Raspberry and on firewall).
If I do a
netcat -u -v 9993
Connection to 9993 port [udp/*] succeeded!
so UDP seems ok.

I have other Zerotier clients behind the same firewall (they are on windows) and they connect fine to other Zerotier networks.
Firewall on Raspberry is disabled.

I have no more ideas. Can somebody help ?

Sorted out. It turned out that during configuration both the br0 interface and the eth0 interface got an ip address. Removed IP from eth0 and set up a static ip to br0 sorted the issue out.
Having an IP on the eth0 interface when part of the bridge causes issues with UDP traffic