When having two items with attribute modifiers that have the same id and apply to the same attribute but require different slots to activate, the game starts behaving in unexpected ways.

Equipping both items in there respective slots only applies the modifier once (as expected.)

Removing only one of these items also removes the modifier despite the other item still being equipped in the correct slot and theoretically applying the modifier (unexpected).

I know that it is not intended to have two modifiers with the same id but it could actually be useful if this bug was fixed since it would then be possible to use an "or gate" for modifiers.
You either have to wear this equipment in this slot or this equipment in this other slot to get the modifier but wearing both at the same time doesn't add to your attribute value again. This has good implications for datapack creation in my opinion.