The most noticeable times this occurs is when you give them strength or weakness and it does nothing. Small does none, medium does 1 1/2, and large does 2 hearts no matter what effect it has applied. Damage changes through weapons are also ignored. This bug goes much further back than the original strength bug post in 2019, and goes back to somewhere in 2018. I do not remember these versions that were affected.

Steps to reproduce:

1. spawn a slime and make sure it is either medium or large sized.

2. do /effect @e[type=slime] strength 999 255 true

Expected result:

The slime should one shot the player and if it has weakness, do no damage.

Actual result:

It will always does it's base damage, no matter the strength or weakness level inputted.