Are you within a condo building or corporate office?
Firewalls may be setup that block traffic of this type. Talk to your network administrator Other problems? Check test.webrtc.org and see if anything is marked as "RED". You can also try different networks and see if that helps.
In the meantime, OBS.Ninja/old is up, and will remain up until I can resolve all the issues with the new release. This may solve your issue temporarily. So if you have this problem , where you see the fullscreen video, but it is just grey and spinning, then it could be a network issue.