Weird dot at the bottom in the macrocellular stage

I noticed this myself as well, and after tweaking things in Godot, I believe that visual artifact is present in the Godot default 3D background. So it is an engine “bug”. We’ll move to using our own backgrounds in the next release (for the underwater part) which won’t have this visual artifact.

It still exists on land.

Well, yes. On land the default Godot environment is used, and in there the same geometry (I presume) is used for the “sky”.