I don’t know how I am always applying the class navbar-fixed-top.
Then just remove the sparkling theme on your site and reinstall the latest version of it.
There are two plugins (one is custom, I guess), a code and a page full of information I couldn’t understand.
You have to use the custom plugin shared in the following reply.
https://colorlibsupport.com/t/fixed-header-on-every-page/#post-37757