When two functions with the same name are ‘extern “C”’ for example, the compiler/linker will pick only one of them and which one is undefined. The choice could even change the next time you build. I’m not sure if compilers/linkers warn about this now but they certainly didn’t warn about it back when I first discovered this on a project.

And of course, the outcome ranges from nothing (if both copies happen to be identical), to slightly off (e.g. one dependency had a slightly older version of the function), to downright wrong (e.g. crash in this case).