A family of Microsoft word processing software products for creating web, email, and print documents.
I should also note that I primarily work on a Mac but with this document, I have opened it on my SurfaceBook, running Windows 10. I just checked and the Surfacebook is running a beta channel version of Word (the latest, I believe).
My Mac is running the current channel and the problem has not resurfaced since I rolled back to an earlier version of the document.
I'm going to make a copy of the document and open it on Windows to see if I can reproduce the issue. I'll report back...