Adding or hiding elements often causes layout conflicts, because UIStackView adds a new constraint at 1000 priority. You have to work around this by bumping one of the other constraints down to 999.
Also recent versions of interface builder tend to complete fail at rendering nested stack views, even though the layouts work fine when you actually run the app.
Also recent versions of interface builder tend to complete fail at rendering nested stack views, even though the layouts work fine when you actually run the app.