Not going to lie, I'm not really sure what exactly is going on here. I have been able to reproduce it in multiple chunks though. It seems to only affect the first layer of blocks above sea level? I'd have to do more testing. Could possibly just be a weird sodium translucency thing, but I couldn't say since this doesn't happen with shaders disabled.

I forgot, here's my settings.
Bliss-Shader-main.txt

This is not the shader's problem actually, if you turn it off you'll see it does that even without a shader.
This is Sodium's lack of translucent geometry sorting. they are going to add this feature in their next major update. just stay tuned for that.