Currently using a Sangoma S500 with four extensions programmed. Have to use the web interface for the time being because I was having issues with EPM.
Basically, when there is an internet connection drop, accounts 2,3,4 attempt to re-register within the 2 min specified registration expiry. However, account 1 takes around 10 minutes to recover. Everything is identical in all four accounts with the exception of the extension number and password. All extensions are chan-sip and the phone is located remotely behind NAT in ipv4 mode. PBX is not behind NAT.
There is often a failed-register timer, as well. This prevents the phone from pounding a server that’s unavailable or possibly triggering some kind of fail2ban, etc. Probably whats happening here. I’d almost be inclined to say it’s wrong for 2/3/4 to re-register immediately. Go look for a setting like ‘register failed timer’ or similar.