Video out doesn't work only in a Zoom call - no where else

[scouffasd]

I have been having an issue with Zoom call video out. It doesn't always happen but has been pretty much the norm lately. When I enter a Zoom call (whether I'm hosting or not) the other participants can't see me but can hear me. I do my calls from an iMac desktop with the latests update of the operating system. My camera is working and I authorize the use of my camera on the call at the beginning. I can see myself in the window, but no one else can. 

My camera works as expected for FaceTime and Facebook video calls. 

This is a big problem for me because I need to do Zoom calls with my customers. I've tried turning off my VPN for Zoom calls, resetting my wireless router before calls. I have tried to get this to work with Safari and Firefox. That doesn't seem to make any difference.

The kicker in all of this is that occasionally, the video works without issue on Zoom calls. 

Any idea of what I need to do to resolve this issue?