Just off the phone with Chris at Canon pro tech support, excellent help provided.
Setting up with WFT E6A for the first time with C300 MkII, and I found that the process was easy to implement. The only issue was that one component was missing - Live View. All other operations appeared normal, including remote control of white balance, ISO setting, record stop/start, aperture setting, focus functions.
After trying different browsers, 2 laptops, restarts on camera, I was eventually advised to do a reset on the camera.
Since the C300 MkII doesn't appear to have a dedicated reset button on the camera body, I did a menu reset (with WFT E6A disconnected). Live view functionality was available immediately after reconnecting the WFT transceiver and powering the camera back up. Although neither the tech person on the call nor myself can tell how exactly this fixed the problem, I thought it worthy of sharing. This issue did not exist in their knowledge base and took us 1.5 hours to work through.
I had the same issue with the WFT E8A today and my C300 mk II and after a lot of searching through the menu, I discovered that the live function on the remote app only works when the magnification while recording is turned off on the camera.