Most Poisons impose the poisoned condition: "A poisoned creature has disadvantage on
Attack rolls and
Ability Checks"
Protection from poison says: You touch a creature. If it is
poisoned, you neutralize the poison...
It DOES NOT say that the poisoned condition is removed.
Do you also rule that the poisoned creature still suffers from disadvantage on Attack rolls and Ability Checks?
Before saying something to the affect of "Well obviously a creature that is no longer poisoned doesn't suffer from the poisoned condition...,"
Keep in mind that you are arguing "An invisible creature still benefits from the invisible condition even if it is visible..."