I'm about to head to bed so I'll get back to this discussion tomorrow, but in the meantime: Victor, maybe it would make sense to reformulate your reproducer as a monkeypatch for _find_and_load_unlocked() that injects the 10 ms sleep from the test case if it finds _frozen_importlib in sys.modules?

That is, temporarily replacing it with something like:

    orig_find_and_load_unlocked = _frozen_importlib._find_and_load_unlocked
    def _slow_find_and_load_unlocked(name, import_):
        time.sleep(0.010)
        return orig_find_and_load_unlocked(name, import_)

That way, we'd hopefully be able to reproduce the failure independently of the slower buildbot.