Woodland Mansion missing some blocks on inside of roof

Confirmed, however the Z coordinate is actually -8192.

Confirmed in 1.11

Confirmed in 16w50a

Not sure if it's the same issue/cause, but something similar happens on a world with seed -1528392416861039717 at (-29223.5, 81, 15937.5) in 1.11.1 (refer to screenshot). The room on the other side is a "Grave room", ID 1x2_d3 according to the wiki.

Affects Version 1.11.1 (thgilfodrol's Screenshot)

Can still confirm issue located at "-1050 90 -8192 on seed -6178286686098098179" as per OP, related missing wall section issue is also still present on 1.11.2.

Confirmed for 1.13.1.

/tp @s -1108 88 -8131 90 -20 on seed -6178286686098098179

Reason for the missing stairs is because the "carpet" structures create those pillars; but have air in front of those, rather than nothing (structure void).
As for the missing block in the wall; that beats me.

Confirmed for 20w21a

Can confirm in 20w51a, using the provided seed and coordinates.

Can confirm in 21w03a.

Can confirm in 21w05b.

Can confirm in 21w06a.

Can confirm in 21w06a.

Can confirm in 21w07a. The provided seed + coordinates still showcase this issue.

Can confirm in 21w11a.

Can confirm in 1.17.1.

I would like to propose we split this bug report into two as the 1 block hole and 3 block high hole are caused by separate issues and needs different fixes. My bug report here handles the 1 block hole which is caused by an air block in an nbt file MC-240221

This bug report can focus more on the 3 block high hole as that's caused by the minecraft:woodland_mansion/small_wall.nbt piece being asymmetrical and not placed right. The 2021-10-31_16.44.20.png I attached to this bug report shows it better. Notice how the small_wall reached the column of cobblestone that marks the end of the 3rd floor's wall on the left side of the mansion's wall always. The 3 block high hole is always on the right side of the mansion wall and that's because the small wall starts 1 block to the left of the right side's cobblestone column.

The solution to filling in the 3 block high hole is to extend the small wall nbt to the right by 1 so it is symmetrical. Then, adjust the code to offset it to the new correct starting position so it is still aligned with the rest of the wall's patterns.

In WoodlandMansionPieces$MansionPiecePlacer.createRoof method, the small roof if statements should be changed to this to this for properly offsetting the newly resized small wall nbt piece. I had to do quite a bit of trial and error to get it working but this offset + the fixed nbt file did solve the 3 block high hole issue.

if (!WoodlandMansionPieces.MansionGrid.isHouse(simpleGrid, l + 1, k)) {

  blockPos15 = blockPos7.relative((Direction)rotation.rotate(Direction.EAST), 7);

  blockPos15 = blockPos15.relative(rotation.rotate(Direction.NORTH), 1);

  list.add(new WoodlandMansionPieces.WoodlandMansionPiece(this.structureManager, "small_wall", blockPos15, rotation));

}

if (!WoodlandMansionPieces.MansionGrid.isHouse(simpleGrid, l - 1, k)) {

  blockPos15 = blockPos7.relative((Direction)rotation.rotate(Direction.WEST), 1);

  blockPos15 = blockPos15.relative((Direction)rotation.rotate(Direction.SOUTH), 7);

  list.add(new WoodlandMansionPieces.WoodlandMansionPiece(this.structureManager, "small_wall", blockPos15, rotation.getRotated(Rotation.CLOCKWISE_180)));

}

if (!WoodlandMansionPieces.MansionGrid.isHouse(simpleGrid, l, k - 1)) {

  blockPos15 = blockPos7.relative((Direction)rotation.rotate(Direction.WEST), 1);

  blockPos15 = blockPos15.relative((Direction)rotation.rotate(Direction.NORTH), 1);

  list.add(new WoodlandMansionPieces.WoodlandMansionPiece(this.structureManager, "small_wall", blockPos15, rotation.getRotated(Rotation.COUNTERCLOCKWISE_90)));

}

if (!WoodlandMansionPieces.MansionGrid.isHouse(simpleGrid, l, k + 1)) {

  blockPos15 = blockPos7.relative((Direction)rotation.rotate(Direction.EAST), 7);

  blockPos15 = blockPos15.relative((Direction)rotation.rotate(Direction.SOUTH), 7);

  list.add(new WoodlandMansionPieces.WoodlandMansionPiece(this.structureManager, "small_wall", blockPos15, rotation.getRotated(Rotation.CLOCKWISE_90)));

}

@unknown, thank you so much for your detailed comment. I've removed screenshots showing the one-block-hole bug and linked MC-240221 as related to this ticket.

Per MC-203453:

I can't seem to find any mansion that is affected anymore in 1.18.
I found mansions with this wall-roof transition at hallways, walls between rooms, and in the middle of larger rooms, none seem affected.

The only problem that seems to be left is a single missing cobblestone stairs block/the wall's pillar not continuing downwards.