Recently noticed an issue on a password protected site I created. If the username/password are inputted incorrectly on the first try, the login box disappears. Only the locked page with note saying "...you must provide valid credentials" shows up. This only happens on mobile. Only way to bring it back is by clearing browsing history/cookies.
I had feedback from a client that said they experienced this same issue on their laptop, so I believe it's not limited to mobile.