I cannot discern whether or not this water shader is from this specific beta version or not. I had not noticed it in previous betas nor is it in the changelog for this latest one. Apologies if this report is old news.
The water shader which physically displaces the waters vertices does not play nice with anyone under the water. Both visual bugs can be seen here in this screenshot.
As you can see; the water mesh has it’s backfaces culled resulting in this odd patchy look when viewed from the side.
Additionally the visible separation line between above and below water on the player’s screen is also completely disconnected from the actual position/displacement of the water.