Working with track changes in Word is very slow or crashes Word for lots of users

I work with in-house and external editors and authors who use and review Track changes and Comments in Word. Within the last 2 weeks or so, work with Word has become almost impossible for several of them, as reviewing Track changes slows down to the point where it takes 10-20 seconds for anything to happen. (Example: 'The Word document has slowed down to the point that I can use it. I have answered all the comments but can't scroll up or down or edit text. Even going through the comments has been painful, clicking on a comment at a time and waiting 10 seconds for the comment to move to the right section, then typing comments and waiting another 10 seconds for my words to appear in the comment box.') This is a new problem - many of my colleagues have been working with Word in this way for many years and never had this issue. It mainly affects people with a cloud-based Office subscription so I assume it's some kind of update that has messed up that functionality. Any ideas or suggestions how to resolve this? One of my colleagues spent 2.5 hrs on the phone with Microsoft who took control of her computer and ended up telling her accepting all the changes would solve her problem (it didn't, and as she needs to review the tracked changes, that was a pointless bit of advice). HELP!