Hi @argo ! Thank you for posting at Auth0 community!
That error seems to indicate that you are running into Brute Force Protection, described here:
For example, if a user attempts to sign in from IP1 and consecutively fails to log in 10 times, then future login attempts for the user from IP1 will be blocked. Other users attempting to log in from IP1 will not be blocked.
Can you also please clarify, are you trying to login with a user email that was deleted a while back? If so, are you also seeing an error “User already exists” for these users? If so, this post might be relevant: "User already exists" error when trying to create a user
Please let me know if that helps. Looking forward to your response!