Did you ever figure this out?

To get full control over the display (and printing) of tracked changes, I suggest that you choose the "All Markup" view. Use the Advanced Track Changes Options dialog box to set all options for displaying revisions in your Word installation.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional

I'm copyediting the document, so I don't want to see all the markup while I'm working on it and I'm not trying to print it. The red line in the margin is convenient as a visual tracker of my place in the document.

It seems switching to All Markup or toggling Track Changes off and then on again fixes the problem, but only for a few seconds to a minute, and then the line disappears again. It's ultimately more of a nuisance than an actual problem, but I'd like to know the cause.

You can choose, in the Advanced Track Changes Options dialog box, to only display the Changed Lines.

However, if "Simple Markup" is sufficient for the needs of your document, you should be able to use it exclusively. I'm not aware of an issue when the Changed Lines disappear. I am using Word 2019 myself and I haven't seen that happen. Are you displaying the document in Print Layout view?

Are you running some sort of add-in with Word or Office?

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional