nether-like generation not working

Hey everyone,

I've got an issue. I've made a dimension and set it to nether-like generation.

At first, it was all fine, the dimension looked basically like nether with different blocks.

But then, something went wrong and the dimension started generating like a bunch of overworld-like caves instead of true nether-like gen, meaning some cascades above big fluid lake and stuff like that, you know how nether looks.

I think it started happening about time I added some structure to that dimension (some weird trees), so I deleted the structure spawn elements and created a new world, but nothing changed, it's still a bunch of awkward caves.

Can someone help me with that?

Thanks.