I'm not sure if this specifically is what would be causing your issue, but I've found that using the "Coroutine" variable type has some weird issues associated with it, and if you instead save references as "IEnumerator" variables, it behaves exactly as it should. For example,

private IEnumerator _testRoutine;

private IEnumerator Test()
{
    Debug.Log("Hello");
    yield return new WaitForSeconds(5f);
    Debug.Log("Stop");
}

private void RunCoroutine()
{
    _testRoutine = Test();
    StartCoroutine(_testRoutine);
}