iOS App Terminating due to uncaught exception with no stack trace (Swift)

Question

I was writing up code for animating UI elements in my app. The app worked fine until I changed the alpha on certain UI elements, when I got this error:

libc++abi.dylib: terminating with uncaught exception of type NSException

There was no stack trace or indication of where the error might be in the output, just a Signal SIGABRT pointing to the AppDelegate class.

The app worked on the previous build and all I changed after that was the alpha settings, which I undid to try and debug the situation. I have tried disabling certain parts of code I recently modified such as Game Center and I have tried setting breakpoints but cannot get the app to work.

My Question - What is this error and where is it coming from?

Here is some code I recently modified if you need to see it:

//This code is called in a Game Center Authentication method
         UIView.animate(withDuration: 0.5, animations: {
                        self.pointsIndicator.center.x += self.view.bounds.width
                       // self.pointsIndicator.alpha = 1
                    })
                    UIView.animate(withDuration: 0.5, delay: 0.3, options: [], animations: {
                        self.pointsLabel.center.x += self.view.bounds.width
                       // self.pointsLabel.alpha = 1
                        }, completion: nil)

View Will Appear:

override func viewWillAppear(_ animated: Bool) {

    //Setup animations
    print("\(progBar.center.x) Before")
    pointsIndicator.center.x  -= view.bounds.width
    pointsLabel.center.x -= view.bounds.width
    progBar.center.x -= view.bounds.width
    masterLabel.center.x -= view.bounds.width

    pointsIndicator.alpha = 0
    pointsLabel.alpha = 0
    progBar.alpha = 0
    masterLabel.alpha = 0

}

UPDATE: I ran the bt command on the debugger. This is the output:

* thread #1: tid = 0x6646da, 0x0000000110607e6e libsystem_kernel.dylib`__pthread_kill + 10, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
frame #0: 0x0000000110607e6e libsystem_kernel.dylib`__pthread_kill + 10
frame #1: 0x000000011063e8fb libsystem_pthread.dylib`pthread_kill + 90
frame #2: 0x00000001103570b3 libsystem_c.dylib`abort + 129
frame #3: 0x000000010fe6243a libc++abi.dylib`abort_message + 266
frame #4: 0x000000010fe86a9f libc++abi.dylib`default_terminate_handler() + 267
frame #5: 0x000000010985359f libobjc.A.dylib`_objc_terminate() + 103
frame #6: 0x000000010fe83c09 libc++abi.dylib`std::__terminate(void (*)()) + 8
frame #7: 0x000000010fe83894 libc++abi.dylib`__cxa_rethrow + 99
frame #8: 0x00000001098534b7 libobjc.A.dylib`objc_exception_rethrow +  40
frame #9: 0x0000000106c07bf1 CoreFoundation`CFRunLoopRunSpecific + 433
frame #10: 0x0000000107d4ac00 UIKit`-[UIApplication _run] + 459
frame #11: 0x0000000107d50e8b UIKit`UIApplicationMain + 159
* frame #12: 0x000000010681423f MathsRobot LearnMaths`main + 111 at     AppDelegate.swift:19
frame #13: 0x00000001102ab6bd libdyld.dylib`start + 1
frame #14: 0x00000001102ab6bd libdyld.dylib`start + 1

UPDATE: AppDelegate:19

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

Answer 1

Credit to jeromeshr over on Apple forums. Was running into this with some Objective-C code called from a Cocoapod from Swift code. If you have the OS_ACTIVITY_MODE flag set as an environment variable, this will block the correct stack trace from showing. It's set on all my apps to avoid an endless stream of non-useful information in the console. Just uncheck the box next to it (you don't have to delete it) while you're debugging.