When creating a custom dimension, players are only able to use "stone_depth" to change the surface blocks of a world when the generation happens above water. when below water, the "stone_depth" acts as "above_preliminary_surface", only generating on the top layers of the world. if there is an overhang underwater with another valid surface below it, the surface below will not be changed by the surface rule. 

According to Misode, a valuable community contributor, the "floor" surface type for stone depth does not work when there is stone>water>stone, only when there is stone>air>water>stone, leading to this bug. he has stated that the surface rule does not have this issue when using the "ceiling" argument, but only when looking at floor types. this prevents ocean worlds with complex noise rules from generating with their proper surface rules. 

I will provide two screenshots of examples in my own project, the first being an area of the world that does not have the proper surface rule due to this bug, and the second being a picture of the overhang that generated above it that is obstructing the surface rule. 

I will attach the data pack that replicates this issue as well, which you can see for yourself by using /execute in to teleport yourself to the dimension abyssalis:abyssalis.