Thank you! That helps me understand why the problem happened in the first place, but I still don't understand why I can't create new links to the correct heading? Why would it revert to an old, hidden, deleted bookmark when I'm giving it a new location to reference? Is there any way to access the hidden bookmarks and update/correct them? (I apologize if that's a stupid question- I know nothing about bookmarks.)

I used hyperlinks because I needed the display text to be different from the actual heading. Many of the definitions are acronyms and have all the words listed, but I just wanted the acronym in the body text. I do use cross references for anything where the exact text of a referenced item makes sense in my sentence.

Thanks again!