@thucuu8x - I just experienced the same issue using the free version, 2 devices (a) Firefox/Opera/Chrome browsers or (b) Android phone. The account is NOT even near its limit.
I get to the login screen, enter the email address. The screen for password entry does not appear.
Logging in via Google account - The screen for password entry does not appear.
Suggested fixes above do. NOT. work. for. me.
What did work? -A password reset.
Both access ways/access via both devices are again working using email as login once I entered a new password.
Hope this helps.
