It only has the one IP address - router/firewall/computer configuration hasn’t changed in about a month.
I will check to see if for whatever reason the firewall may be stopping it, but it is strange that it would start to do it now when it worked for several days.
Just checked the firewall and we don’t block any outgoing requests for this protocol.
Final update - I re-registered with Skype and it started working and enabled consistent NAT in the firewall. I think the NAT got changed on us.