From what I understand, getting Mode #2 requires you to know the name of your soul slayer. Since Kenpachi doesn't know, it's safe to know that his soul slayer is stuck on Mode #1. As for Ichigo's soul slayer, I think it's just stuck on Mode #2. Why it's stuck like this, I dunno, but maybe Ichigo is special, based on what we've seen with the hollow mask appearing constantly as well as seeing the white Ichigo in his inner self.