taking pictures underwater with iPhone 11pro inside a Seawag

Hello. I am in Puerto Rico snorkeling and seeing wonderful fish. I would like to take pictures or video underwater. Given that the iPhone 11pro is water resistant but not waterproof, and that I will be using it in salty water, I bought a Seawag pouch, which is inexpensive and seals hermetically allowing me to operate the touch screen without problems... outside of the water. I can't figure out what is happening underwater. If I have the phone inside the pouch on the surface, all touch commands work fine. As soon as I deep it under the surface, when I touch the screen to take a shot or start the video, the phone does not respond. I take it above the surface, and it starts working again. Is there any issue with water pressure, even when the phone is only one foot under water, that makes the buttons stop working? The instructions in the Seawag specify that if I have problems with the home button in iPhones 7 or 8, I can use AssistiveTouch. I tried this in my iPhone 11 pro but the problem persisted. Any suggestions?