Your description seems consistent with a problem of the antivirus, that has blocked the program after the 1st run. Reinstall with the antivirus disabled, and configure the antivirus to exclude the whole Addon Manager folder from scanning.
Another possible issue, is that your or some of your addons are mistakenly set FSX to run in one of the Compatibility modes, like XP or Windows 7/8 mode under Windows 10. And this is wrong, and will reduce performances.
Our installer will automatically remove that setting, which might explain why the program starts on the first run after running our installer, but as soon the wrong compatibility setting is restored, it won't on the next run. Sometimes, Windows itself set a Compatibility mode, because some program (likely another addon), crashed the sim, so Windows thought a Compatibility mode is required, but it wasn't, it was just a bugged program that crashed.
Either this, or the antivirus issue, are the only reasons I can think of which are compatible with your report.
If this is not the case, have you tried restarting Windows after start of the sim once ? Does it work then ?