Hello,
Sorry to hear about that.
Actually, the Mobile Sticky Navbar doesn’t work if the Maintenance Mode is turned on under the Theme Settings > Maintenance: https://snipboard.io/KNLSME.jpg
So, kindly make sure that you have turned off the Maintenance Mode from your Site under the Theme Settings.
If you are right now Customizing your Site and Maintenance Mode is needed then don’t worry, you can remain it open till you Customize your Site and once it’s done, you can disable it and then you would be able to see it.
Hope this helps !
Best Regards