Hard to select alternative 2FA method when U2F is primary

When using U2F as primary 2FA method it is very hard to choose an alternative.
The U2F prompt show immediately after entering the password.
I then have to cancel the request and it reappears after a very short time. As a consequence it is almost impossible to hit the "choose an alternate method" button.

The issue names no file or test; start by reproducing sign-in with U2F as the primary 2FA method and trace the screen shown after password entry. Done means the U2F prompt no longer repeatedly blocks selecting an alternate method.

Written by the indexing model from the issue text.