Xcode 12.0.1: Code works on iOS 14-Simulator but not on iOS hardware

I'm having an unsolved bug in my code. The following code-snippet is working well within the simulator but not on a real iPhone device (tested on an iPhone SE 1.gen and iPhone 8, both with iOS 14.0.1.
The line "if let nnSData = NSData(...)" is still working within the simulator but not on real Hardware.

Could it be a bug in NSData? Or a bug in iOS? Or do I have a security problem with user rights of the file containing the data I want to read?

Comments would be appreciated.

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static func loadBaseaArray() -> [Basea]? {
        let fullPath = URL(fileURLWithPath: urlpathAa.path)
     
//the following works in Simulator only::::::::::::::::::::::::::::::::

        if let nnsData = NSData(contentsOf: fullPath)
        do {
            let data = Data(referencing:nnsData)
            if let result = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) {
                return (result as? [BaseaClass])?.map{$0.basea}
.......
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