SIP Info Report shows 2 lines UNREACHABLE?

These 2 lines on the same IP Network outside of the Main Network only seem to work periodically. They can call out anytime they need to but trying to call them fails as long as it says UNREACHABLE. I have tried resetting the IP Tables in freePBX and re-entering the DYN.COM account.I have over 30 phones outside of our Main Network that are set up the same way work just fine. The one thing I do notice are the ports keep changing on those 2 lines every so often through out the day and sometimes change to ports that work, where as the other ports on the phones that do work do not. Could this be the FireWall on their end?