contact form 7 giving error with cache plugin

Hi Team,

I am using Contact form 7(Version 5.0.2) and W3 Total Cache(Version 0.9.7) in my website. I am using multistep form and when you go to next page of- https://www.bunkr1482.com/nu-stp1/ the form did not get submitted and after checking source code only i have found that ajax error is coming like – “Unexpected token < in JSON at position 0”. After going through FAQ page i changed cache garbage collector time to 3600 sec but still getting same error and form submission is stopped.Please check this issue and reply me ASAP.
Thanks.

The page I need help with: [log in to see the link]