I’m running a gun boy build on FL4K with a high pellet count Stagecoach, and whenever Wutan’s top half detaches from his body and flies around, when I fire enough shells that normally fling enemy, it flings the Wutan upper body and causes it to glitch out of the map. I can’t clear the boss with this build because this has happened to me about 20 times now. I’ll provide a video for this later.
I have had this happen too and I’m on XB1.
It is a known bug and when I asked about in one of the hotfix threads I got this response: