That is not an i-MSCP topic. Check your Web applications and your PHP parameters.
Sometimes apache response time is more then 10 seconds and frozen. I created a script for restart apache, when the response time higher 10 seconds. It was work, but It is not finaly solve.
Instead of creating a script that restart Apache like a pig, try to understand why the response take so much time. You should really check your PHP configuration and make sure that there are not too much long processes running at the same time (most of time, they are PHP cron jobs run through HTTP). Don't forget that if for a specific user, there are a FPM pool of 6 childs max and that there are 6 PHP long processes running for that user, all other requests will standby as long as one child will not be available to treat them, or as long as the timeout is not reached.