After further investigation, we have tracked down the root cause of the login issues affecting Android users recently.
The problem was caused by an update we made to our login system which unintentionally logged users out of their existing sessions. Some Android users then got stuck in a login loop when trying to sign back in.
Most affected users were able to log back in normally, and the issue has been resolving itself as new sessions are created. We have now put a fix in place to prevent Android users from getting stuck in a login loop, and are monitoring it closely. We have also taken steps to ensure that a similar update cannot cause this kind of disruption in the future.
We apologise for the inconvenience and for the confusion caused by our initial update.
Thank you for your patience.