It looks like there is workaround for this problem. When GIMP 2.10 is used to load/open, the image (i.e., Page 1), of the defective tif file that it has created (per above discussion) it can then export to another tif file which seem to be free of the defect. Insofar as the tif format preserves the full quality of the image, I'm thinking, this second copy is as good as the first. Unlike the defective tif file this secondary instance can be opened by all of the viewers at my disposal without incident.
Speculation is that this removed whatever role the xcf file, from the prior version of GIMP, played in creating the problem.
Speculation is that this removed whatever role the xcf file, from the prior version of GIMP, played in creating the problem.