Turns out, I changed the annex requirement for residential sectors in another mod I used to test my mods. And I had totally forgotten about it.
Well, it should work now.

the new feature created problems when you were below the 100 pops.

Added two new sectors that are unlocked when reaching 100 pops. Due to how residential sectors seem to work, all future residential sectors add a new sector after you reach the difference between the last and the one prior. In this case 100-100=0, meaning, each 0 new colonist will add a new sector, aka, once you annex a sector, you can annex the next without the need to grow your population.
Also incidentially adds 2 more sectors you can annex at the same time...