As of yesterday, Monday 05/10/2021, I have been unable to login to my sandbox testuser_ account using the exact same credentials as I have used to login to the same account many times over the past several weeks.
It doesn't even get me to the point of password entry, as soon as I hit 'Continue' after typing in my username (beginning with testuser_), it says "We ran into a problem. Please try again later." I've also tried with "TESTUSER_...".
What can be done about this and what can I do to prevent it's recurrence in the future?
Thank you for your time.