Hi @rkrous,
Thank you for writing in, the one-page navigation should work without any additional custom code, would you mind removing (commenting out) all the custom CSS and custom JS you added on Theme Options? I see a JS error on your site so that might be it.
If the issue persists, please do testing for a plugin conflict. You can do this by deactivating all third-party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Remember to clear all your caching features (plugin, server-side, CDN, and browser’s cache) for the changes to apply immediately.
If all else fails, try the solution provided here.
Let us know how it goes,
Cheers!