As stated in the title, mspt takes a really hard nosedive (>=220mspt on an R5 3600 with nothing else but the game stressing the CPU) when entering the nether for the first time with sync to overworld turned off. It was so bad that even in singleplayer I had to break blocks several times before the game actually registered it, something which so far I've only ever seen when playing on servers under heavy stress.
It seems after a few minutes it's fine again, which makes me think the server process gets confused with all but one chunk missing but still having the lava floor that is technically still spawnable for striders and the likes(?)

Also the nether roof for "blank" chunks is at Y=128 while generated chunks have their roof above that at Y=256, which makes it very easy to access the roof area. In my case I'm not overly bothered by that but I can imagine that this is not desirable in every setting.
Not sure it might play a role that I also use Incendium in the pack to prettify the nether.

On other note, I know it's possible to do so with resourcepacks, but I'd really appreciate if it was a config file option to toggle if the nether should be affected at all by the mod.