These actions include:

• A skeleton being converted to a stray
• A mooshroom being sheared into a cow
• A pig being converted to a zombified piglin
• A villager being converted to a witch
• A hoglin being converted to a zoglin
• A piglin being converted to a zombified piglin
• A piglin brute being converted to a zombified piglin
• A zombie villager being converted to a villager
• A villager being converted to a zombie villager
• A husk being converted to a zombie
• A zombie being converted to a drowned
• A large slime converting to smaller slimes
• A large magma cube converting to smaller magma cubes

The bug

If a warden gets angry at a certain mob (see list above), and said mob transforms into a another mob before the warden can kill it, the warden will not remain angry at this mob and will need to become aggressive toward it a second time.

How to reproduce using the skeleton as a test case

My setup isn't great - there's definitely improvements that could be done to make it easier to reproduce. A screenshot is attached: a skeleton is spawned within the powder snow and a button is used to spawn a warden behind it via command block after the skeleton starts vibrating, such that it offers enough time for the warden to get angry without landing a killing blow. The repeating command blocks are to kill arrows and get rid of the darkness effect.

Expected results

The warden would remain angry even when the targeted skeleton becomes a stray.

Actual results

It loses its target.