Inside of the lava room of a nether fortress the fence's above fail to connect to the sides, Reproducable by running /place structure minecraft:fortress and going into the room with the 1x1 lava and looking at the fence's on the top of the hallway, you'll be able to see that they dont connect to the sides

Also it affects all 1.20.x versions

using the below diff on `NetherFortressPieces.CastleEnterance#postProcess` fixes this

- this.generateBox(pLevel, pBox, 5, 8, 0, 7, 8, 0, Blocks.NETHER_BRICK_FENCE.defaultBlockState(), Blocks.NETHER_BRICK_FENCE.defaultBlockState(), false);
+ this.generateBox(pLevel, pBox, 5, 8, 0, 7, 8, 0, Blocks.NETHER_BRICK_FENCE.defaultBlockState().setValue(FenceBlock.WEST, Boolean.valueOf(true)).setValue(FenceBlock.EAST, Boolean.valueOf(true)), Blocks.NETHER_BRICK_FENCE.defaultBlockState(), false);