Login issues

On quite a few of my sites I’m having problems logging in. I keep getting a “You do not currently have a Simple Firewall user session.
Please login again.” Sometimes it seems it lets me through after a few tries, other times it puts me on freeze so I can’t login again for another three seconds. The safer login is a great feature so I’d rather not disable it, any idea what may be causing it and how I can fix it? Thanks for your time!

https://ww.wp.xz.cn/plugins/wp-simple-firewall/