Before I've upgraded to Xcode 8 I haven't seen this error in such case. I have different Navigation Controllers. For all of them I see an error Frame for "Navigation bar" will be different at the run time. Navigation bar "Expected: width=384, Actual: width=375. In reality these Navigation Controllers doesn't have Navigation bar. Navigation bar exists for subviews. Anyway I could solve it by tick and untick the checkbox Shows navigation bar in Attributes inspector. But unfortunately every time I reopen Main.storyboard this warning appears again. Also if I click on yellow triangle and then on update frames nothing happen.
Best Answer
Warning will disappear if you change the property "Simulated Size" to "Freeform".