Strange SIP Registration Port for Remote Extension

FPBX reporting strange port in peer report for remote extensionand I can’t discover the source. Router set to 5060, SIP set to 5060, phone set to 5060. Help, any ideas?

That is the remote port. Usually always random and completely normal

Hum, OK. Two things. A few days ago I experimented with mapping and alternate port in my router to 5060 and then setting the Extension Module port setting to the alternate port. Unfortunately this some how altered my VOIP trunk service port which stopped it working. Before that reconfiguration, the my peer report showed the remote extension port as 5060 and the phone worked.

Now, I have changed all settings back to 5060 and the peer report shows 61633 and the phone does not work. Something has changed and I have not been able to discover what.