I saved the navigation file to an experimental file, stripping everything except the critical start and end of file lines and one destination link. After saving that minimalist file, I uploaded it to the server, then refreshed the site. I was relieved navigation was again viewable. I decided to keep that file as an initial backup file and experiment with a newer working file. With the newer file, I added a notification line—"troubleshooting in progress"—which would stay viewable until I resolved everything.
My methodology shifted to replicating the information as applicable, referring to an older writing sample of the AHOT site. Processing a few lines each time, I would add the html line item codes and back slashes, upload the file, then refresh the page. I finally encountered the offending line that caused the navigation menu to disappear—"AHOT Members' Resumes". It occurred to me that maybe the apostrophe might be "abnormal" (my word). After googling for html code for an apostrophe and finding "’" (& # 8 2 1 7 ; without spaces), I proceeded to replace the symbol in both places. Another save, upload, and refresh. Woohoo! I sure was happy to see the navigation again!