and restarted the sim before beginning a second scenario. Then GSX reverts back to being inactive and in trial mode.
With "inactive", you mean it's not working at all, not even in Trial ( the Trial airports ? ). If this is the case, then your problem doesn't anything to do with activation, it's just that Couatl on the 2nd session didn't start for some reason, so the Addon Manager indicated "Trial", because the Addon Manager doesn't do anything to check the license, it asks Couatl and, if it's not there, it will always say "Trial".
A most common reason why Couatl doesn't start on a 2nd session, it's because you started a new one too quickly after the previous one. Even if the program icon has disappeared, it will take a bit more before the simulator has closed all the program it started, and this will take more, the more add-on you have that must be sent notifications to close, and it will take even more if your system is stressed by too many add-ons and too high-settings, and it will take even more if you don't have lots of RAM.
If you want to get a feeling how much it takes to REALLY close the sim in your system, try to open the GSX Control Panel while the sim is running, and keep an eye on the button that says "Waiting for the sim to close". Exit the simulator, and notice how long it takes for the button to become available to Compile. THIS is when is absolutely safe to restart a new session.