Why all the element moved when adding a constraint in storyboard?

问题

I design all my element nicely for a prototype cell of tableView,but whenever I add a new constraint for my element,all element just moved and become like image below:

It happen often,may I know why is this happen and how to prevent it?

EDIT :

For example,before adding constraint it look like this

The white part in the center is a stack view,so I set it to leading = 0 and trailing=0.And then I add a constraint inside the stack view to leading=0 which it align with the stackview all element moved again and become like this:

As you can see,all thing just disappear.Why is this happen ya??

The constrainst that I adding is like below:

Status Label.leading = leading

It happen also when I set the spacing of the stackview to 10,all the element also gone.

Edit:

I have a red arrow appear in storyboard,I suggest the Content Priority Ambiguous,but I after change the priority as to 252 as suggested,all element just disappear again.

回答1:

Remove the bottom constraint of the bottom most element attached to the content view and add all your remaining constraints & with stackView spacing , then re add the bottom constraint again

来源：https://stackoverflow.com/questions/48140066/why-all-the-element-moved-when-adding-a-constraint-in-storyboard