Fortunately I've never had this crash my app - I'm lucky in that it just litters the debug console with messages. I've reported this to Apple via their new feedback tool but haven't heard anything...
I see this in iOS 13.2.3 (I just checked) as well as iPadOS 13.3 beta 2. I'm begining to think this is a debug statement accidentally left in production code...
My app still functions correctly (so far as it is implemented - I haven't completed the code in the background thread yet). I can add a quick and dirty test, though, to see if the error is correct and the thread is running or not.
Same with iOS 13.3 beta and Xcode 11.2.1 GM 11B53. the interesting thing is the identifier number changes over the course of sending my app to the background and reawakening it...
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I strongly suspect you are right that this was different that what others have reported but wanted to let people know what I found just in case. In my case, the second view controller disappeared after appearing for less than a second - I was unable to invoke the UIActivityViewController (which should have been a hint to me) to press the save button.
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I don't know if this will help or not, but I found what was causing the issue for me: I copied a button on the main View Controller to repurpose it to open the secondary View Controller with the UIActivityViewController. The button I copied was originally for closing the main View Controller. When I copied the button, Xcode didn't remove the message to the code to close the View Controller. In order to view the secondary View Controller, I used a direct segue (control drag to the new View controller). So, when I pressed the button to view the View Controller with the UIActivityViewController, the direct segue fired and showed the secondary View Controller long enough for the button to then call the close code on the first View Controller, which somehow made the second View Controller close.After I removed the incorrect action in the button, I was able to see the UIActivityViewController without any issues. (Well, there was one issue: I needed to set popoverPresentationController?.canOverlapSourceViewRect to true.)I hope this helps!Stuart
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I see this as well. Very frustrating... Unfortunately, no solution yet.
