Hi Myles,
Thanks for the clarification. First of all, please make sure that you have correctly setup your navigation by following this guide (https://www.youtube.com/watch?v=TRXHOYjSGRk).
Upon further investigating, I see the following error JavaScript error on the console log when loading your site.
InvalidStateError: An attempt was made to use an object that is not, or is no longer, usable
Please disable all of your 3rd party plugins except Cornerstone and check to see if you’re experiencing a plugin conflict. If the issue issue is resolved, then you need to activate your plugins one by one to see which plugin causing this issue.
If you’re still having issues, then you will need to disable your child theme by activating your parent X theme. If the issue is resolved, then you need to check your child theme customizations to identify the cause.
Further if you have added any custom JavaScript codes into your custom JS area, you need to remove them as well and test your issue further.
If you’re using a caching plugin, please purge your server cache and disable it temporarily until you isolate your issue. Make sure to clear your browser cache as well before testing.
Let us know how it goes.
Thanks!