Before David’s and Mike’s suggestions came through, I made a duplicate of the file and just started deleting pages, one stack at a time, to see if I could flush out the culprit … kinda like before the days of Mac OSX, when you had to turn extensions on and off to isolate the source of a problem. I deleted as much as I could, including as many Parent pages as was allowed by the program. No change.
Next, I tried Mike’s trick. No change. But saving as an IDML and opening up it up again DID indeed clear out the red error icons, but I was unable to Save As the file back to an Indesign 2025 file — perhaps that’s par for the course when one saves to IDML? Attempting to save back to 2025, my screen just went into a hang. Fortunately, the file has no issues exporting to PDF, so unless this has really piqued your interest, I’m going to write it off as a corrupted InDesign file — sort of a digital of Lyme disease — and just live with it. Thanks, though, for your suggestions.