Well, one possibility is that you don't have pynivision installed. I didn't have it installed, and there was no way to know that it was using the 'dummy camera' instead of the real camera.
When I install pynivision, I get a "Connection reset by peer" error. The problem is that when the LabVIEW dashboard connects to the server and it encounters the wrong version of networktables (we haven't upgraded to 3.0 yet), it disconnects from the camera. When I block the NetworkTables connection, then the camera works fine.
It's pretty terrible, the CPU usage is at 51% without the robot code actually doing anything (as compared to ~7% without the camera code). I wouldn't recommend using it, and I suspect we'll remove the camera stuff from the next release.
I'm tracking this issue here:
https://github.com/robotpy/robotpy-wpilib/issues/172