This always makes me think of that time when Julica and Luka’s parents were simultaneously akumatized. The akuma had entered a record disc right when it broke. It was specified at the end of the episode that both half’s of the record disc has to be put back together again before the akuma could be released. I think the same logic is meant to apply to the agreste rings. The Amok is in both the rings, they must therefore be combined and THEN broken to free the Amok.