After updating to 20w28a snapshot existing pillager outposts stop spawning pillagers.
To recreate this do the following:
- Create/join a world in 20w27a or below.
- Locate a pillager outpost.
- Save and quit.
- Join the world again in 20w28a.
- Remove the hostile mobs so new ones can spawn. I set the world to peacefull and back to normal difficulty.
→ No new pillagers will spawn at the outpost and the outpost doesn't show up using the /locate command.