Oh this... I had something weirdly different recently. On a digital ocean account, all of a sudden I couldn't log in. Apparently the login page was updated and said my email adres was invalid. Which is weird cause I definitely logged in before. I used the + trick with Gmail, so I thought this was the issue, icw. new login page. Wasn't the case. Apparently my DNS service which also does filtering, blocked part of their CDN, also part of the email validation javascript. Turned that off, could log in again.