IOS Facebook SDK 4.1: didFinishLaunchingWithOptions returning false

I have a Swift app that was using the iOS 4.1 SDK successfully and until last night everything was working correctly. Then things got sour and the SDK seemed to stop working with my application. I haven't made any changes to Facebook app settings or app code. All the required information is present in the info.plist file and AppDelegate calls the appropriate methods such as

var fblaunch = FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)

      

        
        
        
      

    

and also the openURL method required elsewhere in the delegate. However, the didFinishLaunchingWithOptions call now returns false for no apparent reason. The login button I installed still opens Safari and displays the appropriate information about allowing my access to Facebook, but when the device returns to my app, it acts like nothing happened to Facebook. What's happening?