This problem has been persistent for a while, just happens every so often at random times, nothing changing. I also do not know how to reproduce the problem, but I\'ll give a de
Here's the easy work-around I've found for this bug:
I do a Find-and-Replace ("search within formulas") for "=" wherever I have the importrange error (=REF!) (or just for the whole sheet) and I replace-all with a "#" in order to make it all be text rather than formula. Then I do another Find-and-Replace over the same area and replace-all the "#" with "=" again. This consistently fixes the issue.