And finally, are you using COTURN? We strongly recommend that implementation of STUN/TURN server. Here http://openvidu.io/docs/deployment/deploying-ubuntu/ you can see described in detail how to properly configure KMS and TURN. Check the 3 configuration files (etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini, /etc/turnserver.conf, /etc/default/coturn) as we state in points 3, 4 and 5. Restart your COURN and your KMS too.