The bug

Parrots while near a hostile mob, imitates them less often. I reproduced this by spawning 5 parrots near a creeper, and most of them just play their ambient sounds while only one parrot imitated the vindicator.

How to reproduce

1. Turn on subtitles
2. Spawn 5 parrots
3. Spawn a creeper
4. Observe
   → The subtitles will mostly display "Parrot talks" or "Parrot flutters", and rarely the subtitle for when they imitate, like "Parrot hisses" for when they imitate creepers.