Summary:
Relates to MC-271000. In 1.9 it was changed that rabbits have 3 health instead of 10. However upgrading worlds from before 1.9 does not update the health of old rabbits. This applies to both max health and current health.

Steps to reproduce:
Use this world to go straight to step 3 2024-05-20_01-19-52_New World-----.zip.

1. Start version 1.8.9.
2. Spawn rabbits.
3. Upgrade the world to the latest version.

4. /attribute @e[type=minecraft:rabbit,limit=1,sort=nearest] minecraft:generic.max_health base get

5. /data get entity @e[type=minecraft:rabbit,limit=1,sort=nearest] Health

Observed results:
The rabbit has 10 health, meaning you cannot one hit kill it with an unenchanted netherite sword.

Expected results:
The rabbit should have 3 health just like newly spawned rabbits.

Screenshots: