It seems that the problem is that `_Py_InitializeEx_Private` calls  `_Py_InitializeCore` and `_Py_InitializeMainInterpreter`. The first one calls at the end `initimport` that in turns calls `importlib._install_external_importers` that sets the PathFinder. Then, `_Py_InitializeMainInterpreter` calls  `initexternalimport` that in turns calls again `importlib._install_external_importers` and therefore we end with two PathFinders in sys.meta_path.

I think the solution is removing the call to initexternalimport in `_Py_InitializeMainInterpreter` as it has been alreade initialized by `_Py_InitializeCore`.