Xcode 7.1 Swift 2 Unknown class in Interface Builder file

In storyboard below the Custom Class field the module is set to None. Change that to your app module or just remove and enter class again, it should set to default like this:

For me the problem was that the class was not part of the Target Membership.Just add the class to the target, and you should see it back on the interface builder.

Still seeing this problem with XCode 8.2.1, but I am able to fix the problem by modify these in the storyboard xml file:

1. Delete customModuleProvider="target" in the viewController tag:

   - <viewController ... customModule="Flights" customModuleProvider="target" sceneMemberID="viewController">+ <viewController ... customModule="Flights" sceneMemberID="viewController">

2. Delete customModule="Flights" customModuleProvider="target" in the widget tag (in my case, a label tag):

   - <label ... translatesAutoresizingMaskIntoConstraints="NO" id="PzF-6K-Hpi" customClass="YZLabel" customModule="Flights" customModuleProvider="target">+ <label ... translatesAutoresizingMaskIntoConstraints="NO" id="PzF-6K-Hpi" customClass="YZLabel">

I find that step 1 is very important too to resolve the crash/warning and cannot be skipped.