Armadillos not spawning in old chunks

I play on a realm that's a year or two old, and we have a savannah biome located right by spawn, so I assumed finding the new armadillos would be easy, but after being in the biome for hours, I have yet to see a single armadillo. I went out to new chunks, and was able to find them, but they were not showing up in previously loaded chunks. As far as I know this shouldn't be intentional, or I am just getting incredibly unlucky idk.