When a trapdoor is placed above water, a player stands on it and makes any form of interaction i.e spyglass, trident throw, block place, trapdoor open/close, etc. The player will clip through the trapdoor repeatedly. For the player it is happening to you cannot see your model clipping but you will see the drowning bubbles flash on and off, for onlookers you can see the player falling through and back up. You seem to be able to move around still as if it weren't happening however it gets loud as you can hear the splashing.

P.s We play with experimental features to enjoy our world's new features. Also on a realm.

I have attached a video below