I've just added Feitian U2F NFC key to my account. I tried to use it in iOS app. After I typed master password a popup with "Two-factor authentication required" has appeared. I've chosen to use the NFC security key. After success authorisation, the same popup appeared. Again I've successfully scanned my key and popup appeared again. Popup disappeared when I've chosen an authorization code. To be sure I've reinstalled the app but with the same outcome.
1Password Version: 7.6.2
Extension Version: Not Provided
OS Version: iOS 13.5.1
Sync Type: 1Password.com