Sticky Header Line

Please see video. There is a faint line that appears now since adding the pro plugin.

https://drive.google.com/file/d/1zB1g1Qj3LkmESnRHxD35b526tmjAaQ8s/view?usp=sharing

I don’t know where this came from and only shows when the plugin is active.

The page I need help with: [log in to see the link]