I created a scene with a custom script. My game mode (Assault) shows up ok in the drop down scenario menu. But when I select it from the drop down menu, it shows every scene, not only the one that is compatible with my script (eg has the correct areas).
What I want is to hide the incompatible ones so it doesn't have the crash risk.

I copied this code from the vanilla missions, I thought it was supposed to run through the scene to see whether it has the required areas.
Am I missing some code?

oh please, if you are going to help, then actually say something.
I've already looked at the sticky. This is not the problem. My scene shows up, but all the other scenes show up as well under my gamemode.

You can add some custom area to your scene, called something like MySuperMissionUniqueArea and then request it from your mission script with:

CC will notice that your mission depends on that area and won't offer any other scenes to play with your activity.

What? This is a quote from the sticky: