When there is multiple failed sign-in attempts the user account get locked in Active Directory. This can be checked with the AD account lockout status. Once the account is locked out, it cannot be used (even with the correct password) until the account lockout duration has passed; or until an administrator manually unlocks the account.
Check AD account lockout status
Administrators can check if an account is locked out in the Active Directory. In ADUC, navigate to user > properties > Account. If you will see following message the account is locked in AD.
Unlock account. This account is currently locked out on this Active Directory Domain Controller.
Check if account is locked using PowerShell
get-aduser -identity testuser -properties * | select accountexpirationdate, accountexpires, accountlockouttime, badlogoncount, padpwdcount, lastbadpasswordattempt, lastlogondate, lockedout, passwordexpired, passwordlastset, pwdlastset | format-list
If the lockedout status is False, then the user account is not locked in the AD. If the lockedout status is Truse, then the user account is locked.