Same problem.
Input email, password
Go background right after push login button
Foreground, showing next view(SMS auth)
=> it doesn't show iCloud dialog nor keyboard even uses becomeFirstResponder.
To avoid this problem,
Remove .isSecureTextEntry of password field in login view
Change contentType of password field from Password to other(like username)
But needed to use .isSecureTextEntry for now thus can't avoid this problem...