Autolayout cannot figure out the height or vertical position of a UIStackView despite having added subviews.
This is a pretty common error and "gotcha" so please see the answer below.
If this is for a UIStackView make sure you are using addArrangedSubview and not addSubview
For me I received the following error:
warning: Ambiguous Layout: Position and size are ambiguous for 'Button'.
Where the button was placed inside a stack view in Interface Builder. The problem was that I had checked "Hidden" in Interface Builder which meant Xcode was freaking out saying position and size are ambiguous. Just uncheck "Hidden" on the stack view and the warning will disappear... Magic! ✨
来源：https://stackoverflow.com/questions/45428953/height-and-vertical-position-are-ambiguous-for-uistackview