6S Plus - almost always in landscape mode when unlocking
My new 6S Plus is almost always in landscape mode when I pick it up and unlock it, even though there's no reason for it to be.
It won't rotate to portrait mode unless I tilt it to landscape mode and back again.
This happens like 8/10 times when I pick it up.
I initially thought I could recalibrate the compass or something to see if it helps, but I cannot find anywhere in the compass app, in settings, or on Google in general which says how to do it.
Anyone else with the same problem?
iPhone 6s Plus, iOS 9.1