When I try to run a build of a super simple project it will work once, but then if I don’t rebuild the scene I get an error with either a build or a launch of “Cannot read property applySceneSettings of null”
I think we’ll need more information than that? That sounds like something fundamental is broken like the engine isn’t loaded.
Hmmm yep that’s all the information I get. Very odd. If I copy the scene and build that then it works for a while.
Scene has 1 model, 1 light, 1 camera and a script to move the model.
Running in Editor? Locally? Can you post the scene?
Is “build” a verb or a noun here? 
Build = Publish in this case! Will get to it in a moment, have a working one right now.