Grass blocks located below structures aren't always converted into dirt when the world generates

The Bug:

Grass blocks located below structures aren't always converted into dirt when the world generates.

This is a problem because this results in lots of blocks updating which causes performance drops.

Here is an example:

Seed: 1359968930092793278
Coordinates: /execute in minecraft:overworld run tp @s 3095.99 62.59 3549.47 164.24 24.30

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look at the grass blocks closely.
3. Take note as to whether or not grass blocks located below structures are always converted into dirt when the world generates.

Observed Behavior:

Grass blocks located below structures aren't always converted into dirt when the world generates.

Expected Behavior:

Grass blocks located below structures would always be converted into dirt when the world generates.