Changing cookie hashes seems to block everyone

I recently made some changes & upgrades to my site.

In order to make everyone log in again to ensure changes are used I voided my cookies by changing the cookie hashes in wp-config.

This however meant that anyone visiting the site receives a brute force ban instead so I had to put the old ones back.

Your insights to this would be much appreciated as I have always previously used that method to ensure everyone logs in again.