This isn't a bug. It is how things rollout with the web version of the game. If you have a Web Only account (an account that you have not logged into a mobile device) this will happen. The web version will update when we require the 12.9 update for all players (which should be happening today).
Alternatively, clear your browser's cache (no need for cookies to be included) and you should be able to log in after. Or you can wait for the update to be required.
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