- Create a flat survival world with commands enabled.
- /effect @s resistance 9000 5 true
- Let monsters hit you.
- Equip some armor.
- Let monsters hit you again.
You do not take any damage because you have the Resistance VI effect.
You take damage in step 5.
If you have resistance 5+ on you won't take any damage as intended as long as you don't have armor equipped.
However if you have armor on you will take damage.
Damage sources tested: lava, fall and mob damage. (Doesn't seem to effect fall damage.)
Does work as expected on java 1.16.
Might be related to