Here's what worked: (1) You may ignore this first item because it probably had nothing to do with the fix, other than it is what I tried first. I exported dark footer. The export downloaded a JSON file where two of the first line items were "name" and "title"; I changed these to Dark-BG-Mix and Dark BG Mix, respectively, thinking maybe the secret (missing) word was Mix. 😉  I saved this file as Dark-BG-Mix.json and imported it back into the Protean mixes. Then I deleted dark footer. This was really not the issue as I have noticed others have all kinds of names not ending in "Mix." I think it might be helpful for someone wanting to clone one of their mixes, however. It helped me feel clean and organized, again. 😀 (2) The real fix was in the browser: emptying caches and going into browser preferences to manage website data and deleting the cache attached to my Una website. Then a refresh of the pages showed my Dark-BG-Mix footer. I must credit "Chris" for his discussion on Una community: https://una.io/page/view-discussion?id=3256 where he mentioned he had to clean caches before he could see his handiwork.