Thanks a lot. I ran your save on the current build, and it seems that it was an issue I unintentionally fixed the other day while cleaning up problems that would spam the log. The NullReferenceException in LightDetector.lightUpdate() was throwing errors every tick on the starting screen (that was also the PlayerMovement error you were seeing, which was only on start screen but also annoying me), so I added a check that also happens to catch the issue on your save (whatever is causing it I can now get a closer look at with your save since it's definitely a bug).
Basically what was happening is that LightController iterates through the entire list of LightDetectors, and at some point early on in that list one of them was broken in a way that threw that exception, causing most of the lights to stop working properly with our visibility system. Thanks again for your help figuring out the issue.