To prevent clickthroughs, add the allowTriggerClickthrough option to the settings in your Site Footer Code Injection area.

DO NOT add this entire code block again, simply add line 5 to what you already have. 

<script>
  window.wmMegaMenuSettings = {
    layout: 'full-width', // full-width or inset
    openAnimation: 'slide', // slide, fade, or swing
    allowTriggerClickthrough: false,
  }
</script>
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Why is there a slight layout shift sometimes when opening a menu?