Login and eliminate reder-blocking problems

Hi

I have two big problem on wp-fastest cache.

First, I can’t login through login page.
When I tried to login through login page. my site just redirect wigh displaying ‘sending request’. but, after deactivating wp fastest cache, it works fine. then I activate wp fastest again. and I tried to login again with wp-fastest cache activating, it works fine sometimes. but later, this problem is shown up again. I can’t figure it out why?
Would you tell me how can I fix it up?

Second, I purchased premium version for speeding up. most problem were eliminate rendering problems for CSS and java script with free version. so, I expected that premium version will clear my issues. but after installing premium version. it’s same, my site still has eliminating rendering problems.

The first reason why I choose wp fastest cache is easy and believe that wp-fastest cache make my site really fast. but now, I faced up two big issues. would you fix it up?

Thank you.

https://wordpress.org/plugins/wp-fastest-cache/