Nav bar distorted during page loading

I’m trying jetpack to see if I can speed up the site and seems a bit faster. The issue is every time I load a page, the top nav bar becomes higher, then shorter, then the menu goes to the left screen stacked up and then in the right position, all this within 1 second or less but quite annoying to see this happening for every page load. On mobile, it does almost the same. I tried to contact but there is to use the form “below” and then there is no form. Can you help? Thanks