AprilShade

This also applies to harming potions thrown by witches, fired by dispensers, or summoned with /summon. It doesn’t apply if the effect is given to an entity directly using /effect.

I primarily tested with Instant Harming I potions, so higher levels or lingering potions may act differently in some cases.

This is also inconsistent with throwing splash water bottles at Blazes and Endermen, which causes no knockback

I presume this was changed at some point, as blazes, endermen, striders, and snow golems all currently take knockback from splash water bottles. The history section of the blaze’s wiki page states this was changed in 1.14-pre 3, though I could not find any other reference, source, or bug report for this.

Based on my tests in 1.21.4, this actually affects all mobs that use the AngryAt and AngerTime tags, not just Endermen. This list includes Bees, Endermen, Iron Golems, Polar Bears, Wolves, and Zombified Piglins. There may be more, but these are the only mobs that are listed on the wiki as having the AngryAt tag. (The wiki claims that Piglins have it as well, but that is incorrect.)

When attacked or provoked, these mobs have their AngerTime set to 400–800 ticks, and AngryAt as the attacker. When the attacker is a Player, AngerTime remains static (excluding Bees; their timer always counts down) while the mob is chasing the Player. If the Player gets out of its range, or enters Creative mode, the mob typically returns to its neutral state, and AngerTime starts counting down at a rate of 20 per second. Should the Player return to Survival mode and enter the mob's detection range before AngerTime has reached zero, and AngryAt hasn't been changed to a different target, then the mob will re-engage with the player.

This differs to how mobs act when fighting other mobs. If, say, a Zombified Piglin and a Polar Bear are fighting, teleporting one 80 blocks away will have them cease hostilities, and have their AngerTime be immediately set to 0. Since AngerTime is set to 0, the two mobs will not resume their fight when reintroduced (unless they're normally hostile to each other, like Enderman and Endermites, or Wolves and Sheep).

Their AngerTime values also decrease while they fight, as opposed to staying constant like they do with the Player.

I also want to comment on steps 4–6 of your reproduction steps. I don't know if it's new, but Endermen will not lose interest by blocking their line of sight, and Endermen will only lose interest if it's daytime. You need to either make sure it's day, or just toggle your gamemode between Creative/Survival for a faster and more reliable process.

It can also be reproduced by dying outside of the attacker's detection range (I think? It may be a different value) and returning to the mob's location before its AngerTime decreases fully.

Can confirm for 1.21.

Jiingy, Yes, that seems to be the same issue. I'll edit this report to focus more on the enderman-specific issue.

This also affects the 1-9 number keys (Hotbar Slots 1-9), F (Offhand), Ctrl + B (Toggle Narrator), C + 1-9 (Save creative hotbar), X + 1-9 (Load creative hotbar)

Additionally, there seems to be some other odd behaviour when holding the 1-9 keys. When not in the inventory, holding these keys seems to queue button presses for after you let go of the button. For example, by holding the 9 key for a few seconds, it will continue thinking you're holding 9 for 1-2 seconds after releasing it, which can cause you to switch to the 9th hotbar slot, show/hide the hotbar in spectator mode, or save/load creative hotbars after releasing the button.

is this the issue? MC-153904

I've noticed this before as well, again like you said it only happens in multiplayer (I've noticed it on both LAN and on a server). To other players I appear normally. I've also had this happen with F3+N, not just F3+F4. This has also happened to me in 1.15.2 as well.

Just happened to my friends on our Minehut survival server, the both died in the nether, got back in under a minute to find all of their items gone.

sorry I try to use the search but usually I can't find what I'm looking for

I spawned in 50 dolphins, all named, but they despawned when the chunk was unloaded

same thing for me!

i also cant redeem my code! it says there are no codes available!

might not help, but I've had a bunch of villagers in a building I made and none have despawned in  the span of a few months. the walls are 2 blocks thick and the only blocks they are able to  stand on  are beds, grass blocks, oak  planks, workstations and chests.

I'm pretty sure this is intended. Same happens will F5, F3, pressing 9 in spectator etc.  

You need to use smooth stone to craft it. regular stone won't work. Put your stone in a furnace again to get smooth stone

I don't know if it's worth mentioning anymore, but they also spawn with these conditions in peaceful. I saw a bunch of zombies trying to spawn in with mab spawning false and on peaceful.

It works fine for me

This has happened to me once. I was in creative and somehow placed a block in  a space that my head was occupying and it put me in crawl (swim) mode.

However whats happening is it will bring the screen up when you let go of sneak as it should, but then it acts as if you quickly pressed it again, immediatly bringing the screen down again despite not touching sneak.

Affects 1.14.2