I’ve actually made some progress with this: It turns out that according to whatever documentation, in this case a random benefactor off of Reddit, Structs and Enumerators have to be in C++ of nativized assets. After nativizing all enumerators of a BP class I had, it gave some clearer errors regarding some other non-nativized BP assets. I nativized those as well, and then I compiled without problems and the program actually started.
So while this was probably the issue, the resulting program is god-awful broken. All “Move To” navigation commands have turned into “Simple move to”, some collision settings are reset for no reason at all, and a multitude of functions return True despite giving an error message that is sent right before it returns False. I have no idea why this is but I’ll keep trying to find the reason it’s broken.
Current theory is that the nativization in itself is broken as hell though.