In a testing world on 1.16.4, I was trying designs for a mob museum, and used renamed spawn eggs for convenience's sake. After leaving that area, I came back to find all but the creeper (which was named with a tag) had disappeared! Confirmed in a controlled environment too, see videos.

I know this issue has been reported before, but previous reports; *MC-162182* and *MC-54556* are outdated (1.14 and earlier snapshots of said version) and are marked resolved, when in fact this still happens in 1.16.4 and no fix is reported in the changelogs for 1.17 snapshots.

How to reproduce: 1. Rename a hostile mob spawn egg with an anvil (Zombie will do, make sure it does not burn). 2. Get an unnamed spawn egg of another hostile mob (Can be the same mob) 3. Rename a name tag. 4. Spawn both mobs and name the unnamed one with your tag. 5. Move 128+ blocks away and head back. Only the tag-named one should be there.

What should happen: Mobs that are named should not despawn regardless of method (unless otherwise specified, e.g. by NBT tags).

What happens: Mobs spawned with a renamed spawn egg are able to despawn.

(Video has been split into several parts and compressed due to file size limits)