I’m on it!
*sharpens Demon-slaying sword.
I was able to reproduce this effect (to a lesser degree) when I loaded the site! It looks like you are using the Montserrat font from Google, and it takes a moment to load from their servers. Before the font loads, the links are displaying in your Body font, which causes the longer Nav Links to shift down to their own row.
My first suggestion would be to reduce the margin/padding of the items in your Navbar. See if this works first. It should prevent it from the drastic shift down, but you may still notice the font change. I’m not sure if you noticed, but the font delay is also affecting your body content.
To fix this, I would highly recommend downloading the Montserrat Google Font and uploading it to Webflow with these instructions.This should speed up the font loading, and hopefully eliminate the effect for text around your site.