That's because your mobile network is blocking the traffic.
Some mobile networks do that.
You haven't said whether this is when using your own server or the running the demos from
demo.easyrtc.com. If you don't see the problem when running the demos from
demo.easyrtc.com, then the solution is to have a turn server that offers a tcp connection over port 443 (that is the least likely combination to be blocked). If you still see the problem when you use
demo.easyrtc.com, then the only solution is to talk to your mobile network provider.