When a project only has @2x images because it only targets retina display devices, atlas Sprite Kit atlas gets the scale wrong with the RGBA8888_COMPRESSED setting to use with P
The atlas image should have the @2x suffix but not the files contained in it.
Won't work:
atlas.png contains theImage@2x.png
Correct usage:
atlas@2x.png contains theImage.png
I'm not even sure Sprite Kit supports PVR textures to begin with. Perhaps try confirming that your setup works with PNG and then export as PVR and try that.
When you do that, be sure to clean your project (Xcode: Project -> Clean) and remove the app from the device/simulator (this step is crucial!) otherwise the bundle will still contain the PNG atlas image and you may be fooled into thinking that PVR works because Sprite Kit may actually load the PNG atlas that still exists in the bundle if you don't remove it and clean your build.