The bug

Endermen which picked up a block can despawn.

Expected behavior

When endermen pick up a block their PersistenceRequired tag should be set to 1b.

Either the tag should then not be cleared anymore, or better there has to be a tag indicating that PersistenceRequired was set by the player and therefore should not be cleared once the enderman places the block again.

How to reproduce

1. Create a Superflat world.
2. Set the time to night.

   /time set night
   

3. Summon an enderman holding a stone block.

   /summon minecraft:enderman ~ ~ ~ {carriedBlockState:{Name:"minecraft:stone"}}
   

4. Teleport away and then back to make sure they could despawn

   /teleport @s ~ ~ ~1000
   /teleport @s ~ ~ ~-1000
   

   → The endermen holding blocks despawned as well