I have two 5C NFC Yubikeys and have been trying to register both in Protonmail, so that I have a backup key available. I can register either one successfully for login, but not both at the same time. They are both showing in my default usb vm. I can successfully attach them to the vm, on which Protonmail is running. I can then enable “Security key” in Protonmail and successfully register the first (either) key and give it a unique name. But then trying to register the backup key by clicking again on the “ + New securty key “ and the “Authenticate” eventually results in timing out without success. I think the problem is Qubes related and not Proton related, but at a loss. Maybe usb? I have tried with both keys plugged in at the same time and have also tried with unplugging the initial key, then attaching the second key to the same usb port.