@Michael_Oborne I tried it on Linux and it loaded firmware fine - build 1.3.580. So I reverted back to rc9 on Linux from one of my dev builds. Went to the Windows computer and tried it and this time it loaded firmware (build 1.3.6794.30567) but it did not load the heli firmware I selected. Not quite sure what it loaded, as there was no H_ params for helicopters, and I got an error when I connected to the board complaining that it did not know what the frame class is.
Reloaded the firmware with QGC and then everything was fine again - got the proper helicopter firmware I selected to install.
So tried it by downloading the firmware first and using install custom firmware. On Linux using build `1.3.580 it installs fine. On Windows with the above noted build it fails to identify the board - it says no response from board.
This probably doesn’t help much, just some experiments I tried here. There is some strangeness with Windows and its DOS-style COM ports that Linux does not use. I’ve been able to load firmware before with MP on Linux while other users have noted their board is not identified, or no response from it, on Windows. I can put that latest build in my Linux dev machine this evening and try it again, but I have yet to ever have a problem with MP on Linux, so it will likely be no different.
Maybe somebody who is more versed in the strangeness of how Windows does things can shed some light on it.