Why my bv9500 pro can't take photo or video at underwater?
It's always out from camera and go back to home menu. Sometime it's not go back to menu but shutter doesn't work.
Anyone can help?

Please perform a factory reset, use the Opencamera app and report back if this solves your issue

Still can't take photos from underwater, I try opencamera application when I want to shoot the screen always freeze. If the phone I pull out from water it's normal again.

Did you perform a factory reset? 

Yes I did

Ok, very weird issue. Definitely.
It looks like an hardware problem related to bad sealing. What I reccomend is to contact your seller to have your device replaced under warranty, as this is the best way to get back a full working -and sealed- unit.