Redirection loop

Sucuri security login not working?

wp-login.php?redirect_to=https%3A%2F%2Fwww.example.com%2Fwp-admin%2F%3Fsucuriscan_lastlogin%3D1&reauth=1

wp-login.php?redirect_to=https://www.example.com/wp-admin/?sucuriscan_lastlogin=1&reauth=1

Sucuri Security – Auditing, Malware Scanner and Security Hardening

How to solve?

Check incognito or private browsing if cookie was the issue. If it works then you need to clear cookies of your web browser.

If you are using Chrome goto chrome://settings/cookies?search=cookie

Search the site and clear its cookie.