Please update 8theme Core plugin to 1.0.19 v (Appearance > Install Plugins) and check versions of all other plugins https://www.8theme.com/download-plugins/
Also, try to disable 3-rd party plugins and then check the problem. Let us know results.
Do you have the issue with contact forms only with our theme or even with default theme activated?
Check the plugin settings or contact plugin author about this issue because we provide support for issues related strictly to our theme or plugins that come bundled with our theme.
Sorry, but we can’t provide you with a solid recommendation about security plugin.