On Jan 9th logins dropped by 50%[1]. The issue has not been resolved and we do not yet know the cause. This is considered a code-red issue.
Most previous login drops have been caused by technical issues, and were resolved within 4 hours.
We do not believe this is a client issue, since the login drop is uniform across all platforms and is present in the one-month hold-back.
We do not yet have any other indication of the cause of the issue. Investigation is being led by Alice Axe and Boris Ball.