I purchased the ring-type accessory for my iPhone 7 Plus, Matte Black, and I really love the functionality of it, while it lasts. On my black iPhone, the adhesive doesn't seem to stay on for more than 2 days before coming off the iPhone. Does anyone else have this issue? I have tried using a bumper case with the clear plastic back and attaching the ring to that and it holds VERY well; it would require a lot of force to pull off. I would rather use the accessory on the naked back without a full case, however. Do the Matte Black iPhones have a different coating than the other colors? My friend has a jet black and a rose gold and the adhesive sticks on those colors fine.