Login error

Hi,

We’ve used this plugin “all-in-one-wp-security-and-firewall” in one of our sites, and apparently we are not able to login while making changes. It logged us out of the session. When we try to log in with valid username and password, but in vain. Could you please advise us on this?
What could have caused this?

https://wordpress.org/plugins/all-in-one-wp-security-and-firewall/