Hello,
Please deactivate all the 3rd party plugins and activate only theme-required plugins on the site, and then check the issue. I am sure your issue will be solved. Then, activate the 3rd party plugins one by one and check which plugin is creating the issue for you.
If the issue remains, please download the latest version of the theme from your account on ThemeForest and reinstall the theme, replacing all the files via Appearance -> Themes -> Add new and let us know if it works.
Best Regards,