Sometimes you can see a yellow warning that appears under the conditions you set in the rule:

Imagine a rule that goes: 

Pause ad set if ROAS < 1.5

The point of that warning is that when you have 0 purchases, the ROAS is going to be 0 too. And 0 is less than 1.5 and hence the rule will be triggered even if an ad set barely started delivery. It can be paused even in the review stage in that case. 

So here it is essential to add one more condition like Spend > $X so the rule won't stop the ad sets right after they started. That should answer it but if anything is still not clear please send your questions our way!

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