basically someone at google thought it would be a great idea to put a 7day security block on anyone that had multiple google accounts in their browser to prevent free users from just making a new gmail and abusing the system. and now - everyones locked out. it comes back to an account identity mismatch problem.
i did a whole technical writeup with proven explanations and solutions on the 16th, and been blasting it everywhere to try helping users understand and remedy the issue.