I just had this problem like today and I noticed that it should be something to do with the Stamina... with TGM(GodMode) I can powerattack as much as I want with no crash at all and when I disable TGM, I can do one power attack (which consume about 60-70% of my stamina) and the second one will crash immediately be crash straight away before the animation ends... Give it a try and see if I'm right about this