I don't know that it is so, but it has been suggested that teams like the Giants and Cowboys, among others, have overcomplicated their coverage schemes in an attempt to disguise them. It has involved mixing m2m and zone coverages, stunting DBs and interchanging responsibilities between corners and safeties.
Feckless blitzing often can make it worse as was the case for both Giants and Cows, last Sunday.
Confusion, miscommunication, however we characterize it, we aren't seeing just poor coverage, we are seeing (blown) no coverage. Frankly, I don't see why safeties should ever be out of position in playing 2-deep zone on obvious passing downs.
Of course, when they did play a lot of simple two-deep zone, it was not received with approval around here either.However, I thought they were doing a very decent job playing Nickel/ Cover 3 on the obvious passing situations, last year. I don't know what reasons they have had to something different this year.
Cheers!