After getting a pillager grinder set up, I killed the pillager captain spawned in the outpost, and they won't spawn after that. I created a copy of the world and went into Creative to clear all entities but they still do not spawn in the area, even after making the area dark and open. There is no problem with spawning for other pillager outposts I found in the world.

The world I am playing on is hosted by another person on iOS.