The bug

The new forgiveDeadPlayers and universalAnger gamerules do not apply to llamas, dolphins, and spiders in the daylight. They will always act as if forgiveDeadPlayers is true and universalAnger is false.

Additionally, the further improvements to neutral mob behaviour were not implemented for these mobs either. As such, they stop attacking you when you leave the world or when you switch dimension / go into unloaded chunks.

Reference: https://twitter.com/henrikkniberg/status/1268765029777772549

How to reproduce

forgiveDeadPlayers

1. /gamerule forgiveDeadPlayers false
2. Summon a llama
3. Switch into Survival
4. Hit the llama
5. Before the llama attacks you, run /kill
   → The llama no longer tries to attack you

universalAnger

1. /gamerule universalAnger true
2. Summon a spider in the daylight
3. Switch into Survival

4. /execute at @e[type=spider] run summon potion ~ ~1 ~ {Owner:[I;0,0,0,0],Item:{id:"splash_potion",tag:{Potion:"harming"},Count:1b},Motion:[0.0d, 0.0d, 0.0d]}

   → The spider doesn't attack you

Logging out

1. Summon a llama
2. Switch into Survival
3. Hit the llama
4. Close and reopen the world
   → The llama doesn't attack you

Unloading chunks

1. Summon a spider in the daylight
2. Switch into Survival
3. Hit the spider
4. Switch dimension or go into unloaded chunks
5. Return to the spider
   → The spider no longer tries to attack you