The Bug:

Grass blocks located two blocks below pale oak or dark oak trees aren't converted into dirt when the world generates.

Here is an example:

Seed: 7555437788059119351
Coordinates: /execute in minecraft:overworld run tp @s 1400.29 115.89 -2414.82 -156.73 6.64

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.

Observed Behavior:

Grass blocks aren't converted into dirt.

Expected Behavior:

Grass blocks would be converted into dirt.