Not sure I get this answer. The OP has a stick-at-top Navbar, not a Sticky Navbar: https://www.swanplastics.co.za/demo/products.htm. The issue is that as an image slides under the Navbar, if you hover over that image, the underlying image, whether on a MouseOver or popup layer comes in front of the Navbar.

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When I make the Navbar stick-at-top Kirst_Rework.xar I get the same error that the OP sees - in the OP example the underlying logo reveals itself and the telephone number scrolls out of view.

When I make the Navbar sticky (and place it on the top of the page); there is no issue, but the only way I can find with stick-at-top and match the OPs design is here: Stick V-top.xar

Gary