Well it may happen for whatever reason. On an aMiSTACX stack give this a try from CLI:
cd /var/www/magento
sudo php bin/magento admin:user:unlock "exampleadminuser"
Just replace “exampleadminuser” with your admin user account.
Another way, is to replace or create a new account from the CLI:
e.g., sudo php bin/magento admin:user:create --admin-firstname=magento --admin-lastname=admin --admin-email=support@example.com --admin-user=admin --admin-password=$uperPassword
Should you still have issues, and have access to email, attempt to reset your password.
If all else fails, reach out to our support.
~ Lead_Robot