The Bug:

Walls within ancient cities can generate in invalid block states.

Here is an example:

Seed: -2284214782727173621
Coordinates: /execute in minecraft:overworld run tp @s 1659.03 -44.00 -1541.22 -145.78 40.55

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look closely at the block states of the walls.
3. Take note as to whether or not walls within ancient cities can generate in invalid block states.

Observed Behavior:

Walls can generate in invalid block states.

Expected Behavior:

Walls would generate with the correct block states.