That seems reasonably comprehensive - a shame those options didn’t help. I’ve asked the software team if they’ve got any ideas.
One more (unlikely to help but worth a check) option from my end is to get the sdp file from http://192.168.2.2:2770/vlc.sdp, and try running it using VLC (VideoLan). It should have basically the same video display as what QGC gets via gstreamer, but doesn’t hurt to try another video player just in case QGC or gstreamer are doing something weird/unexpected.
It may also be worth trying another topside computer if that’s possible - although given it worked fine with the RPi camera then I don’t expect it’s likely to be a magic bullet.
I’d be interested to know if the same issue occurs via our companion beta software, which uses a different program for managing cameras than the current companion. If that does happen to solve the issue I still wouldn’t recommend using it in production/for work purposes (given it’s intentionally unstable beta software), but at least that would be another known benefit of the way things are going 
I appreciate your understanding that we don’t have infinite resources. We’ll continue suggesting things to try while we can think them, and hopefully we can help you solve the issue, but if we run out of ideas before the problem is solved then we’ll just have to ask you to try a different camera