Hello and thanks for your patience on this. These behaviors (no video and attendee issues) almost always stem from firewall or NAT (Network Address Translation) configurations. The lack of video originates in problems assigning and listening on dynamic port numbers due to that network configuration.
Do you have a TURN or STUN server address set up in this domain's configuration? If not, I recommend testing this change using one of the publically available STUN/TURN server deployments that are available including Google's to see if this resolves the problem. Please let me know how that works out for you. Have a good one!
Kyle Kerst
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com