Hi @cilefen
Thank you so much for the prompt request to provide details on the issue.
1) The site is not a newly-installed site
2) It had been upgraded to Drupal 10 from Drupal 9 more than a year ago
3) One of users requested the admin to reset her password (as forgot password email is not working)
4) She was using the account without any issues about a month ago
5) When the admin is about to reset her password, he noticed that the email field is empty, and it is no longer a required field
Site has few password/login related modules including Password Policy (which set password expiration, length, character types) etc.
eaajithe → created an issue.
I had the same issue after migrating the site from 9.5.11 to 10.1.5. Finally found that the issue was with Varnish cache. I cleared it. Site came back to normal