There is no easy way to determine which client in a p2p connection is having the connection issues. If you have clients that you know work with others, you can attempt to connect this known client to the client that may be having issues in order to isolate the computer that's having issues.
Depending on your browser some information can be looked at but it is quite advanced. chrome://webrtc-internals
If you need more help I can give some ways to look at the logs of the webrtc connection, but I would try a known working computer first against the iffy client.
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com