I have having this issue this morning, tried refreshing to no avail, closed and re-opened browser.
Had to use a "Reply" button on the thread to force the log in screen to appear.
I have PM'd Cordovan, but there is no link to the Web Admin to report issues.
After days of reasonable speed, this morning the forum server is dog slow at loading the home screen, over 30 seconds for the initial load - I could see it responding to each TLS handshake, it was THAT slow.