After performing a fresh install of Azure AD Connect, and having healthy synchronization for over a week, today an error caused synchronization to stop. The status is no-start-credentials and the incidents Status lists failed-authentication - Invalid Credentials Error Code 0x31. I have come across this article "https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-change-addsacct-pass" but during the install I did not create the account that I see in the properties of the on prem connector. This account starts with MSOL and the password field is empty. I am pretty sure this account was created automatically during the install and I can confirm that no changes were made to this account and it is not disabled. I know I can change the password for this account and assume that it will work but I am unsure what could have changed to cause these credentials to fail. Has anyone seen this issue before?