Here’s an excerpt from the original (it’s 5 pages long) file in edit mode:

The highlighting is also visible in preview mode
But when I export the PDF, the highlighting in this section is gone
I can reproduce this very easily:

I don’t use any third party plugins (safe mode enabled).
My core plugins: File explorer, Search, Quick switcher, Graph view, Backlinks, Tag pane, Page preview, Command palette, Markdown format importer, Templates, Outline, Word count.
Hope that helps.