Once upon a time I found this forum helpful. Apple engineers would even chim in - if no one else.
Now it seems it is a place to let issues die.
I have this same issue, though I'm loading the textures myself. What's frustrating is that everything looks fine in the inspector. All the texture levels are there, all are correctly sized, and all are the same internal format. So I don't know what it's complaining about. It seems like it all started after the lastest xcode 8.1 update, but I could be wrong there. It's interesting that it's hapenning with GLKit, as this indicates it might not be something in my code after all.