I know the reason of this warning and how to solve it: to give a preferred width to the label.
The problem is that, when I click that warning, I don't see any label/view/viewcontroller selected. The storyboard opens and that's it. There are many view controllers with many views in my storyboard. How can I find out which label is causing the problem without iterating through all the view controllers manually? When I click the warning, I expect it to take me to the view causing the warning, but it just opens the storyboard.
Here is one way to find the specific label that is causing this warning: