I was going to post a new thread, but I'll answer here. There seem to be common problems getting the video connection to start, and various work arounds.
Today I had an experiment. The camera link is a 5Ghz wifi connection, so I used a tablet to connect to the camera (Yuneec provide a CGO3 App so you can control the camera from your phone or tablet). The connection is just a normal wifi connection, so you set that up first and then go into the app.
Now the interesting thing was that the tablet (a very reliable Samsung), 'saw' the camera network then lost it. Then it connected again. Then disconnected. Finally it managed a stable connection and everything worked reliably. This is whilst standing three feet away from the 'H.
My suspicion therefore is that the problems are with the camera module, not the ST-16 or the antennas we're using. It appears to have problems setting up a stable ad-hoc network. Though I didn't look too closely, I suspect the camera reset itself at least once while the tablet was trying to connect.
So far in flight, I've had very few problems and have got some awesome video. However, I'm hoping Yuneec can clear up why that start-up time can occasionally be minutes long, and perhaps provide a firmware fix if it's not a hardware fault.