Bedrock v1.20.62
Villagers located in the room 14 blocks below the surface under my house (healed from zombie villagers) make illagers consistently spawn underground. Explanation by GoldenHelmet makes perfect sense. I literally was unable to find them even by switching the copy of the world to Spectator mode and searching for 20 minutes.
v1.20.62
A week ago this started happening to me on a local world quite regularly, usually for the first load after starting the app. After loading I'm at the spawn with literally nothing. If I immediately leave the game and load the same world again, everything is back to normal.
This doesn't feel to be resolved.