Shulkers in End City entrance get "replaced" by end stone blocks

The bug

When and End City is generated and the entrance is below the end stone, the two Shulkers that should be in there get "replaced" by end stone blocks, and the Shulkers themselves teleport somewhere else within the area.

To reproduce

1. Create a world with the seed -2399401086576537194

2. Run

   /execute in minecraft:the_end run tp @s -7265.52 61.00 -1211.52 244.05 7.80