We have reports of 2 different people not being able to do a P2P mode video call while connected to the US cellular carrier T-mobile. Calls over other cellular networks seem to be working fine as far as we've tested. We're using Twilio's STUN/TURN servers and it is otherwise reporting that TURN is being used so I think TURN is set up correctly.
What version of WebRTC is included with v3.3? I've seen some mention of recent fixes possibly relating to IPv6 support that may be applicable to T-mobile. For example  that was fixed in M53.
Other than IPv6, does anyone know what might be specific to T-mobile?
The version of WebRTC included in v3.3 is M54. Could you please help check whether the client connected to T-mobile can successfully connect to signaling server (Peer Server). So we can know if this issue is caused by signaling or PeerConnection. Thanks.