[tor-relays] OR port no longer reachable

Guys,

I've been running a relay since many months without issue (Tor 0.2.6.9 on CentOS 6 fully patched)

Since a few weeks, my OR port is no longer reachable without apparent reason (Dirport remains reachable on port 9030)

[warn] Your server (xx.xx.xx.xx:9001) has not managed to confirm that its ORPort is reachable. Please check your firewalls, ports, address, /etc/hosts file, etc.

Nothing changed on my network nor on the config...

Both Dir & OR port are open and routed properly (Nmap checked from the Net)

Selinux & firewalling are disabled, nothing but localhost in /etc/hosts...

I'm kinda puzzled... Could you tell me where I should investigate further?

Thanks!