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@meaton Was there a specific code level question that was asked here or did you end up getting your issue resolved? No, I didn’t resolve this issue. I didn’t provide code in the ticket, because reproduced the same issue without my application. 
I opened iOS native settings app and start switching between 2 companies Wifi AP, sometimes WIFI connection stuck for 2 minutes. So I think it is an iOS issue. I don’t know why but if you disconnect from the freeze Wifi AP and connect one more time, the second connection is fast. But then if you continue switching between network issue reproduces again

I see the same message when calling the reloadData UICollectionView method. Sometimes the app doesn't reload cells, func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell  is not called, contentSize in that case is incorrect and equal to the sum of estimatedItemSize. As result UICollectionView is empty. Strange that it reproduces only from time to time. Before xCode 13 and iOS 15 I haven't seen such issues.

Have the same issue. But I found strange app behaviour on iOS 15.0. When the iPhone screen is locked and the app was closed(terminated), in 10 minutes iOS 15 opens it automatically in the background mode (didFinishLaunchingWithOptions, UIApplication.shared.applicationState == .background, the screen is still locked), keychain returns null, the app starts sending requests to my server (see requests in the Charles proxy). Then when I unlock the screen, I don't see that my app is in the background mode, but when I tap on the app icon, the app opens, didFinishLaunchingWithOptions is not called. Tested on iOS 15.1. Print logs into UserDefaults. Maybe somebody knows how to disable this background feature?

Have the same issue. But I found strange app behavior on iOS 15.0. When the iPhone screen is locked and the app was closed(terminated), in 10 minutes iOS 15 opens it automatically in the background mode (didFinishLaunchingWithOptions, UIApplication.shared.applicationState == .background, the screen is still locked), keychain returns null, the app starts sending requests to my server (see requests in the Charles proxy). Then when I unlock the screen, I don't see that my app is in the background mode, but when I tap on the app icon, the app opens, didFinishLaunchingWithOptions is not called. Tested on iOS 15.1. Print logs into UserDefaults. Maybe somebody knows how to disable this background feature?