There were definitely compilers that used things like data-structures with an unstable iteration order resulting in non-determinism, and people went stopping other people from doing that. This behavior would result in non-deterministic performance everywhere, and combined with race conditions or just undefined behavior other random non-deterministic behaviors too.

At least in part this was achieved with techniques that can be used to make LLMs to, like by seeding RNGs in hash tables deterministically. LLMs are in that sense no less deterministic than iterating over a hash table (they are just a bunch of matrix multiplications with a sampling procedure at the end, after all).