I tested it on 3 seeds, on Minecraft 26.1.2, with the skyvoid_worldgen_single_lava datapack. It could (and I would assume probably does) affect the other worldgen datapacks, and maybe also on other versions, though I haven't tested either of those theories.
In the following screenshots you can see what the bug is, and in each screenshot I wrote in chat the details of the issue on that particular seed.

I tested it on 3 seeds, on Minecraft 26.1.2, with the
skyvoid_worldgen_single_lavadatapack. It could (and I would assume probably does) affect the other worldgen datapacks, and maybe also on other versions, though I haven't tested either of those theories.In the following screenshots you can see what the bug is, and in each screenshot I wrote in chat the details of the issue on that particular seed.