I think identifying what is making you stressed will help, maybe draw a mind map of potential triggers of stress in your life and think about things that might be lacking which could help with stress, i.e needing more sleep. Most of all though, don't beat yourself up every time it happens, sometimes it's inevitable, overthinking about when it happens will make it worse. When it happens, try to train your brain to not worry about it, you're very lucky that it's mild. Most non-stutterers will have similar experiences when they are very stressed.