If you run NFCTagReaderSession.invalidate () after the NFC has finished reading, it will take 2-3 seconds slower for iOS 14 to call back didInvalidateWithError than for iOS 13. The verified app was created with xcode 12.4. The device for iOS 13 is iPhone X. The device for iOS 14 is iPhone 11. In iOS13, it takes 0.01 [s] from calling invalidate () to the callback method. In iOS14, it takes 2.913 [s] from calling invalidate () to the callback method. I don't understand why iOS 14 was slow.