As the title says.

One possible version of steps to reproduce this issue:

1. Set render distance to 2, simulation distance to 5
2. Create a single Swamp biome world with seed `-572638717796585636`
3. `/execute in minecraft:overworld run tp @s 37.50 68.00 -21.50`
4. Set render distance to 11, keep simulation distance as-is
5. Wait for the chunks within render distance to finish loading
6. `/fill 240 64 -32 255 80 -17 minecraft:air replace minecraft:brown_mushroom` and notice it replaces roughly 9 blocks
7. Repeat all the steps above from step 1 but set render distance to 12 at step 4, notice it replaces no blocks (or a lot fewer)

Notes: This is also reproducible on every biome that allow brown or red mushroom to generate naturally on the surface of the world.