The entire toolchain is non-deterministic. People also do stuff to make it worse. For example the compiler backend is multi-threaded and spits out data in what

The entire toolchain is non-deterministic. People also do stuff to make it worse. For example the compiler backend is multi-threaded and spits out data in whatever order, doesn't matter normally because they designed it that way. But in a determinstic scenario you have to change that. Then you have to worry about timestamps in PE headers, macros in code, other tools messing with things, etc... Then you have the issues of wanting to cache, that's where things like pathing come in to play.