My site has a top bar and a nav bar with the site menu. Strangely enough, after a few pixels of scrolling down, the content part of the site jumps up. I think this wasn't doing this initially, but I must have changed something in the template settings to start this behaviour. The jumping happens on desktop and mobile alike. What could be the reason for it?
[EDIT: the link to the site was removed, because it became irrelevant for this question after the website experienced an overhaul. As the portion of the website pertinent to this question could not clearly be identified, none of it can be posted here in a sensible fashion. This question is essentially a dead end, but I can't remove it myself. If you can extract value out of the answer kindly provided, you're welcome to do so. Otherwise, I'm sorry about this dead-end-situation. Good luck with your jumpy header navigation or top bar stuff.]
Do I need to change/add something in the CSS? I found stuff about content jumping, but it's all about third party content being loaded later, AJAX modules, and so on. My issue here is different, as the site is all loaded, but as soon as I scroll down a few pixels, the content jumps up quite an amount.