Mobile Header Loading

Hi there, I purchased a theme called Mintie (https://themeforest.net/item/mintie-arts-crafts-wordpress-theme/35010289) from ThemeForest which includes your header and footer plugin. Everything seems to work great except on mobile devices. If I load the site on a mobile phone and don’t actually interact with the site then the header appears to load full screen. It is only when the first interaction with the page happens, be that a finger taps or the user starts to scroll that the header then displays correctly. My concern is that because the header seems to load full screen to start with, it gives the impression that the site hasn’t completed loading and people may navigate away or wait longer than needed before interacting with the site. Is there anything I can do to correct this issue? Any help you can offer would be appreciated

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