KVO: Could not demangle keypath on iOS 10.3.4 iPhone 5

Question

So i was working on private framework that uses camera (so this framework is tested with a device) and decide to use some KVO. i set the minimum version of iOS to 9 in my project.

when i tried to integrate it with the bigger project, it works fine with device iPhone 8 or above and iOS 12 or above.

But when the project is released to public, i have crashes:

Fatal error: could not demangle keypath type from '10QRIScannerAAC': file /BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-1001.0.82.4/swift/stdlib/public/core/KeyPath.swift, line 2611

this trace is from crashlytics and i don't have the specific device to investigate by my self

the stack trace is hidden because the project is obfuscated

the crash report show that it only occurs on iphone 5 with ios 10.3.4 installed

the code that used KVO:

class ScannerVideoCapture: NSObject {   
   @objc dynamic var metaDataStringValues: [String] = []

   //Some logic that modify metaDataStringValues.....
}

public final class Scanner: NSObject {

    @objc dynamic private var scannerVideoCapture: ScannerVideoCapture

    private var scannerValueObserver: NSKeyValueObservation?

    // Initialization, setups, etc.......

    //MARK: Private Functions
    private func registerLocalNotification() {  
        scannerValueObserver = observe(\.scannerVideoCapture.metaDataStringValues,
          options: [.new], changeHandler: {[weak self] object, change in
            guard let dataValues = change.newValue else {
                return
            }
            self?.delegate?.didReceiveDataFromCapture(urlStrings: dataValues)
        })
    }
}

so, is it iOS faulty? or is it the iPhone 5 in specific? or is my implementation just plain wrong?