I am having the same problems in one of the iOS apps since the restriction works in Xcode 7.x but not in Xcode 8, so I found some problems to solve it. You will find the following steps.
1) Open the storyboard in Xcode 8 , then a pop-up window dedicated to choosing the initial appearance of the device, select one of the options and click "Select device". Please find below GIF view for the same.

2) When you make your changes, select the storyboard, go to the “File inspector” section, in the “Interface document” section, select the “Open” field and apply Xcode 7.x After that, a save pop-up window will appear, so when prompted, select "Save and close." Please find below GIF view for the same.

3) Close Xcode and open the application.
Changes to the storyboard will be saved, and the storyboard will work the same as on Xcode 7.x.
Hope this works for you.
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