Steps to reproduce
Load a world with simulation distance set to 4.
Place a dispenser at Y = 150.
Fill the dispenser with creeper spawn eggs.
Stand at Y = 100.
Use a command to place a redstone block next to the dispenser, to activate it.
Expected result
The dispenser spawns a creeper, and the creeper falls down to you.
Actual result
The dispenser spawns a creeper, and the creeper instantly despawns.
Original summary
Dispenser doesn’t dispense mob if player is 49.5 or more blocks below dispenser.
Original description
I have a basic tower with sticky pistons and red stone blocks to activate a dispenser at the top of the world.
When I put a spawn egg in the dispenser, it only spawns if I am within 49.5 blocks below the dispenser.
The dispenser is at y255.
When I activate it standing right next to it, it drops a mob and the mob falls to its death.
When I activate it from y206 or below, there is a little blip on the screen but no mob falls.
When I activate it while standing on the top slab of y206, the mob drops.
When I activate it while standing on the bottom slab on y206 I get nothing.
I placed water for the mobs to land in to test in case there was some weird glitch happening.
Same result. Mob lands in the water unless I am standing below y206.5.
I even double checked that it wasn’t a display glitch (because 1.16.101 mobs are buggy af) by doing the kill command and seeing what mobs are listed.
This confirmed that when I am standing 49.5 blocks or more directly below the dispenser, no mob drops. I also confirmed that the dispenser does in fact release and suck up a water bucket from as low as y124, so this distance issue is unique to mob eggs.
I discovered this on 1.16.101 and it remains the same for 1.16.200.
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GoldenHelmet
Is the world where you are experiencing this on simulation distance 4?
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Sure enough, the simulation distance does affect this behavior. I tested it at sim dist of 4, 6 and 8.
Worth noting: when I activate the dispenser from beyond the simulation distance range, no mob appears nor does a drop happen (no rotten flesh on the ground) but the egg count in the dispenser does decrement.
Also worth noting: when I activate the dispenser from within the simulation distance range, I watch the mob fall past and then disappear somewhere between me and the ground, and no mob drops appear on the ground.
I tested further with water: with water at the ground level, I have confirmed that after a mob falls a certain distance it does indeed disappear and no mob drops appear. I activated the dispenser from within the simulation distance range and watched the zombie fall past me, then disappear rather than land safely in the water.
Thank you for mentioning the simulation distance. I never considered that it also applies vertically.
Is it intentional that mob eggs would behave this way yet water buckets dispense from any distance? Also, the dispenser does release other entities from any distance. I tested with a piston, which landed on the ground as expected.
GoldenHelmet
What you're seeing is the combination of 3 things:
Mobs spawned from spawn eggs fired by dispensers are not persistent. This means they immediately despawn when in chunks on the inner edge of simulation distance, or when beyond a spherical radius of 44 blocks from the player on simulation distance 4, or 128 blocks from the player on higher simulation distances. In your original test you were seeing the spawn-then-immediate-despawn when the dispenser activated > 44 blocks from your position.
Mobs are only rendered up to about 60 blocks away. When you see mobs fall past you and then disappear on higher simulation distances, it is probably because they are falling more than 60 blocks from your position. They will also despawn at 128 blocks if there's that much space between you and the ground, but you can't see that directly on the higher simulation distances.
Redstone updates, including the dispenser activation, occur anywhere within simulation distance of the player. That's why you can activate dispensers to empty water buckets in places where mobs instantly despawn.
Of these factors, the only one that might be a bug is (1). Mobs spawned by spawn eggs used directly by the player are persistent (cannot despawn), so it is arguably inconsistent that mobs spawned by spawn eggs fired by dispensers are not persistent. For that reason, I will update this report around that issue specifically and leave it for developers to say whether that is working as intended.
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Cool. Thanks!