The bug

If an entity outside of the player's chunk is loaded, an invisible version of the entity will remain after saving the world.

Steps to reproduce

1. Create a new superflat world using the preset "Redstone Ready" (easier to reproduce with no other entities in the world)
2. Teleport outside of spawn chunks

   /tp 10008 56 8

3. Press F3+G to view chunk borders
4. Without moving outside the chunk you are in, place an armor stand across the chunk border
5. Leave and rejoin the world
6. Remove the armor stand
7. Try to place a block where it was standing
   → Notice it cannot be placed
8. Leave and rejoin the world again
   → Notice the armor stand reappears

I attached two videos of how to reproduce the bug as well.

Notes

• I haven't been able to reproduce this 100% of the time; I'll update the ticket if I find that there's another factor playing a role in this
• This only occurs outside of spawn chunks
• This only occurs with entities outside of the player's chunk
• This first appeared in 19w08a
• After pushing the invisible entity out of the chunk with a piston, then reloading the world, I received this error:

  Wrong location! (628, -8) should be (629, -8), apg['Armor Stand'/3353064, l='Entity Testing', x=10062.74, y=56.00, z=-120.50]