Well if it’s an assertion failure then it’s something they didn’t expect should happen, so didn’t pass it through as an error to output to the user. Which isn’t much help to you now, since clearly, it is happening.
I’d suggest rather than jumping into debugging UHT, first just try commenting out various bits of reflection-related code in GBAIController.h and see if you can get it to compile. That should help you narrow down the cause.