Attached is an image of a ruined portal which generated in a lava sea, with seed and coordinates attached. It can be seen that there were stairs and slabs generated exactly level with the lava ocean, causing weird gaps as the spaces containing said blocks were not also filled with lava, like what happens with water.
There are two solutions for this:
(Lazy solution) If a stair, slab or other such block is detected to be replacing lava, make it generate as either a full block or lava to not cause the lava level to look weird
(Preferred solution) Change the waterlogged block state from a boolean to something that can support three different states, as to allow for lava to occupy these blocks, eliminating the lava level weirdness this way by having the blocks to be lavalogged.
有可能和你想的不一样万一是mojang新加入的特性呢translation：It may be different from what you think, in case it is a new feature added by mojang