Weird jumping behaviour of Navigation Menu Header

Hi there,
We are using WP 4.7.4, Enfold 4.0.5 and WC 3.0.6
Recently, we noticed some weird behaviour particularly noticeable when navigation within the WooCommerce section of the site.
As you move from product to product, the Navigation Header drops by about half a centimetre briefly exposing white space and then jumps back up to its position at the top of the browser. It’s actually becoming quite annoying, and i wondered if anyone out there had a take on what could be causing this kind of behaviour.