The data fixer has trouble with items obtained by using Ctrl + Pick Block on a filled flower pot with a flower, sapling, dead bush, fern, mushroom, or cactus before version 1.13. Chunks containing these items will be regenerated by the data fixer, and if the item is in the player's inventory, the data fixer will crash the game.

How to reproduce:

1. Create a world in version 1.12.2.
2. Go to the Nether
3. Place a flower pot
4. Plant a cactus in the flower pot
5. Press Ctrl + Pick Block on the flower pot
6. To avoid the game crash, place a chest and place the item in it. (When you hover over the flower, sapling, dead bush, fern, or cactus in your inventory, it will display " (+NBT)"). Alternatively, you can drop the item and then remove it from your inventory.
7. Try opening the world in the latest version

Expected result

Chunks containing this item would load correctly.

Observed result

Chunks containing this item are regenerated. This will be easily noticeable because the chunk no longer has the old Nether terrain. If you skip step 6, the game will crash.