I noticed that sanctums can mess with the generation of both vanilla and JNE structures. I found a campsite generating in the middle of a sanctum, another campsite partially floating above one, a regular fossil completely floating in the air, and multiple fossils that generated inside of a sanctum but seemingly aren't there at the same time (Teleporting to them just brings me to empty space if that makes sense)

due to how minecraft generates structures, conflicts like these are unavoidable unfortunately. but I'll try and see if I can at least prevent mega fossils from generating here