I am having the exact same issue, I am using the plugin on the innov8tive studio press theme, the moment I install your plugin the menu disappears and just like Karen said ,a vertical list appears on the subpage menu. Its the exact same issue. Is this plugin not compatible with the innov8tive child theme? I am can’t put a link because I had to un-install the plugin in order for the menu to come back. What was the solution for this error?