As per the title - new chunks in my current Nullius world (which has been migrated over several mod versions) are being replaced by laboratory floor.
In the imgur link attached below is a screenshot showing what I mean.
I have zoomed out extra far by using Infinizoom. Circled in red are the laboratory floor chunks; in green are normal correct chunks; in yellow are chunks yet to be modified? (if I drive closer they change into bad chunks).
I've also attached my world's save file.
I do hope that this is fixable, since I'd like to continue my run; as this is a fun pack!
https://imgur.com/QpPwcIN
https://drive.google.com/file/d/1ozcYzAYJpC7BVJXCzj1yibG804f82XQ8/view?usp=sharing

Nullius doesn't do anything interesting with terrain generation, apart from requiring the Alien Biomes mod. I doubt this is coming from Nullius. What other mods do you have installed?

I took a look at your save file, and you have a bunch of other mods enabled, including one called "Laboratory Floor World". Looking it up on the mod portal, it's described like this:

"Simple mod to place lab tiles on newly explored sections of the world completely devoid of water, decorations, stones, ores, water, crude oil or anything else not suitable for those in lab coats. Now with 3 ways of impossibility!"

Disabling that seems like a good place to start for solving this problem.

Well this has just turned embarrassing.
Yes, the mod I had enabled was the one creating the issues.