Thanks for the offer Granky. I will preserve with DT 5.7 and try to find out the source of the problem if it comes back. I am moving on to new collections of images so maybe the problem will be resolved.
Not a problem Terry. Now that I have figured out how to convert the overnight files into portable copies of darktable, I can play with the development versions without risking my installed copy. Because the portable’s config files share the same folder as the portable program, there is no risk of upsetting the installed version. Best wishes, David