What would cause multiple iphone 7s to freeze for single user

I have an end user who after receiving her first iphone 7 started experiencing issues where the phone would freeze or apps would close by themselves. We updated iOS, did factory reset and eventually changed her out with another phone. Shortly after that one started displaying the same issues. We again jumped through all the hoops and eventually swapped her out with another iphone 7. All was well for a short while and again this new phone doing the same thing. Only thing I can think of is that user is restoring phone from icloud. Would that carry over some sort of corruption and jack up each phone?

Thanks