Thanks for following up, Rahul.
I think it was being caused by CSS settings. It had gone away and then came back (with a different warning) and now is gone again. The only thing that I changed was the CSS.
If it happens again, I’ll be sure to make a recording and share it.
Something worth noting – UXP only supports valid tables (unlike a browser which will try to fix things up). So it’s possible that CSS could get in the way of things here to cause the table layout itself to become invalid… which would then cause these types of errors.