While testing on how to pickup ghasts with minecarts, I found that some heights are "cursed" as a minecart cannot pickup a ghast where it will at others heights. That happen on versions 1.12.2, 1.15.2 and 1.16.1.

The bug

If a minecart is more than 2 blocks up from a vertical sub-chunk border, it will never pick entities located in the vertical sub-chunk below the border.

How to reproduce

1. Place a soul sand block at Y=15
2. At Y=18, make a 3 by 3 blocks square rail line floating around the soul sand
3. Spawn a wither-skeleton on the soul sand
4. Launch a empty minecart on the rail circle
   → The minecart will not pickup the wither-skeleton, but it will if the setup is make one block offset vertically

Code analysis

From analysis on Minecraft java 1.15.1:

The bug comes from the getEntities functions in net.minecraft.world.level.chunk.LevelChunk. These functions will look at sub-chunks only 2 blocks down and up from a given collision box; so it can miss entities taller than 2 blocks.