As mentioned in the RT, can I suggest to roll back to 6.1.2 then proceed the steps below?
Allow all inbound traffics during the testing.
Start Network Capture. Please go http://<BalanceOne IP>/cgi-bin/MANGA/support.cgi -> Network Capture -> Start. You may use Wireshark if your traffic volume is high (In the case of Network Capture only captures traffics for few seconds).
Make a Voip call.
Stop Network Capture until the session is complete.
Please let us know what is the source and destination IP during capturing if possible.