Admin Log in 404 error

Hi, first time to submit question on this forum. Sorry if I made some serious mistake…

Anyway, I’ve installed WP Fastest plugin and activated.
Everything seemed fine until I was kicked out of the admin (timed out), then, when I tried to log back in, I got 404 error. Site was nicely working, but I was not able to log in as Admin.

I contacted my host server, spent 1.5hrs to solve the problem.
At the end, once your plugin is disabled, I was able to log in again.

I’d like to use your plugin if possible, but I’m afraid to activate now.
Is there known issue (which I couldn’t find in the past threads) for similar problem? If so, what can I do to solve it?