The game exe.xml method used for the autostart is not reliable in general. Apps are not always launched as far as I have seen. I would suggest you to use the FSUIP bat file instead (it launches both FSUIPC and game). I can confirm that FSUIPC works because I have been using the previous version with beta for several weeks. Now there´s a new version anyway and it also works with SU10. It works if you launch it either before game or when game is already running (e.g: during a flight).
Important hint: you don´t need to run anything as admin for FSUIPC to work but if you do it then all other things need to run as admin as well (game, any other apps which are launched by FSUIPC itself and other apps which will be talking to FSUIPC).
The bat file can be simplified and just use something like this (replace the path with the one where you have it installed):
cmd.exe /C start F:\FSUIPC7\FSUIPC7.exe
cmd.exe /C start shell:AppsFolder\Microsoft.FlightSimulator_8wekyb3d8bbwe!App -FastLaunch
Cheers