A note for people searching for solutions.
I’ve finally tracked a published display issue (badly disrupting nav bar and multiple other elements) in the published site down to an empty embed element.
The embed element contained ‘commented out’ custom css - so not having any effect on the site in the designer or on the published elements targeted by custom css.
Several random, unrelated elements adjacent the embed in the navigator were completely disrupted on the published site.
The only solution was to delete the embed.
The only reason I’m posting this is because it took hours to resolve the issue. I didn’t think it could be the embed because the code contained was commented out and therefore inactive.