My iPhone 7+ has recently started having an issue when I try to use my camera in the regular photo mode. It just flickers and is really dark - won't focus on the subject I am photographing (and this is in normal light; not darkness). I can switch to video and it's fine, and even to the other types of photos, but on the regular one it does this flickering. It isn't every time, but it's at least once every few times I try to use it. Anyone else had an issue like this?