So after editing the my.cnf file to optimize the database, I went and did a reboot.
While waiting at the /wp-admin portal of a particular website on this server. I kept hitting CTRL+R to refresh it
It’s possible that I hit it too many times too quickly, and was put on some kind of banned list? As now I am getting this 403 forbidden - openresty error when trying to visit the domain name.
EDIT - I’m guessing it’s like Fail2Ban or something because I am now able to visit the website.
However, I would still like to know the tech behind this so I don’t get myself permentantly banned from one of my own websites one day.