I’ve continued trying a number of other things but the issue I have continues depending on browser and browser percentages no matter what I do so its possible its not entirely my CSS
Still tying to find solution but running out of ideas so might put site online so others may see whats going on.
I however just went and had a look at your demo site again to test one of the issues I previous overlooked and its also doing it.
When you have the sticky menu showing and minimise the viewport to 768 or 769px the menu shoots from the right to left before transitioning into the mobile-header
It happens using various browsers and percentages. Edge, Firefox and Chrome Try 100% and 125%. Both recreate issue depending on browser used.
Plus the other issue I have also isn’t consistent across browsers and or browser percentages indicating its potentially not my sites CSS either.
Check it out