This is all about your wrong editing/customizing of codes. We have seen that you have added the <button> tag in an <a> tag, also included href to index.php file. Please check out the screenshot as reference http://prntscr.com/gs6vn7 That’s why, the button redirects to the index page when you click on the button.
You will find out the issue, when you will compare your website code with our template code. Please recheck & compare carefully your website menu code with our template menu code to fix the issue.
We are really sorry to say that, we are unable to assist you with this issue, when the issue raised for your wrong editing/customizing of codes. This is because, it’s not included our item support. We are only available to assist you on those issues, if our template has an issue to fix.