I know the problem!!!

okay. you can't preserve trigger on alliance or else it will keep "reminding" the zergling that its an ally everytime you tell it to attack. So. You need to have set alliance status only once with player 7 and if you are preserving the trigger it won't work. If you need to preserve it then give it like a 1000 milisecond wait and then preserve it so the zergling has more time to move.
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Its better to put it on a switch or change the conditions so it will only run if you are unallied.