I think the floofs above me summed up the possible issue pretty well, but I may as well add some.
Be sure to keep the tab open, do not close it, but if you still have issues, try closing the game itself and relaunching it, with the login page still launching; or just spam the login button until it registers.
It also wouldn't hurt to signalboost the login thread if other people you know are unable to access the game.