UIStackView - layout constraint issues when hiding stack views

This is a known problem with hiding nested stack views.

There are essentially 3 solutions to this problem:

1. Change the spacing to 0, but then you'll need to remember the previous spacing value.
2. Call innerStackView.removeFromSuperview(), but then you'll need to remember where to insert the stack view.
3. Wrap the stack view in a UIView with at least one 999 constraint. E.g. Top, Leading, Trailing @ 1000, Bottom@999.

The 3rd option is the best in my opinion. For more information about this problem, why it happens, the different solutions, and how to implement solution 3, see my answer to a similar question.

I had the same problem and I fixed it by giving the height constraints of my initially hidden views a priority of 999.

The problem is that your stackview applies a height constraint of 0 on your hidden view which conflicts with your other height constraint. This was the error message:

Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x7fa3a5004310 V:[App.DummyView:0x7fa3a5003fd0(40)]>",
    "<NSLayoutConstraint:0x7fa3a3e44190 'UISV-hiding' V:[App.DummyView:0x7fa3a5003fd0(0)]>"
)

Giving your height constraint a lower priority solves this problem.