Captcha doesn’t reload

My Site is hosted at WP Engine and it provides an inbuilt Cache facility, for the users, on live site only. I’ve used this plugin with contact form 7 and when the site goes live, the captcha stops re-loading, on every load of page.
Even when users prints an incorrect answer for the first time, and then re-print with correct one. It didn’t work.
Form never submits, at any case.
Please help!