Same problem here Yusri.
Math captcha doesn’t always play well with other code above it on the Contact page.
I had a Google Map shortcode above my math Captcha on the page. Aaaand, the Math Captcha wouldn’t work. Once I took the map off of the page the captcha worked fine on all browsers.
Math Captcha likes to have the body of the page all to itself. Any other code above it- especially other shortcodes- can BORK the whole thing.