Same as MCPE-141499, but for mansions. The steps below are sufficient to double most of the illager spawns in a single-player world. In a multiplayer world the over-spawning can be massive, as encountered in this livestream, where dozens of illagers spawned. (Watch from 4:48:02 to the end.)

Steps to reproduce (updated 1/13/2025)

1. Import the attached test world.
2. /tp -7000 120 -10920
3. Check the scoreboard counts.
4. Delete the world from Minecraft and then import a fresh copy of the test world.
5. Set render distance to 14 and turn on the autosave icon in video settings.
6. /tp -7000 120 -10720
7. Face north (-Z direction) until you can see the woodland mansion render.
8. Fly in the +Z direction to about Z = -10600.
9. Wait or fly back and forth a short distance on the X axis until the autosave icon appears.
10. When the autosave icon appears, sprint-fly in the -Z direction until directly above the woodland mansion. If the autosave icon disappears before you stop over the mansion go back to step (4).
11. Check the scoreboard counts.

Expected result

There scoreboards in step (3) and step (11) should match, showing 1 evoker, 18 vindicators, and 7 allays.

Observed result

There are many more evokers, vincdators and allays in the mansion. In the repro video linked below there are 2 evokers, 40 vindicators, and 14 allays, and you can see that the 2 evokers spawned in the same room.
https://youtu.be/J9yh5VmWJ1c