I bet that deal had generic terms in it like “all parties will promote peace through their actions” blah blah blah. If you violate the spirit of an agreement, it’s off. It’s not just the words that count.
Remember that this deal happened while both parties are supporting opposite sides in Russia’s attack on Ukraine. Both Iran and the US are very careful to not be directly involved in the fighting, they just provide weapons.
A Hamas spokesman indicated that Iran was directly involved in planning this attack, further inflaming the situation in Palestine. That’s why Iran is being investigated: because they are directly increasing the violence. Plus even providing weapons to non-state actors is a big no-no in international relations.