Nothing is "random", GSX is either activated or not. The only thing that can make you think it's random, is if you run MSFS with a Windows user account with limited permissions, so you are in fact running it as a different user than the installer (which activates GSX), because the installer always runs as Admin.
So, if you are running the sim with a user with limited permissions, GSX will revert in trial, because the activation is by user, not global, so the solution is to be sure your normal windows user account has admin permissions.