relies on undefined behaviour that just happens to pan out differently between the two iPad versions That would make sense I suppose. I have just been struggling to figure out what the difference would be between the two devices, since they're very similar, and since the OS version seemingly can vary without making a difference. They're using MDM on all of the devices, which also I have no access to. What networking API are you using? URLSession? It's using dataWithContentsOfURL which I believe is using NSURLSession. It's a legacy app that hadn't been touched in years.

Fair enough. It will be hard to confirm what the problem really is, but this is worth a shot. Thank you both!