Thank you for reiterating what I wrote. Yes, you understood what I've tried to communicate. The web link in the citation details on Ancestry, I think, is an artifact of an earlier version of the source citation that had been created via Ancestry and later converted in FTM using the aforementioned template. Now that I think of it, I did not create this citation from scratch. Perhaps that's the origin of the problem.
I will try your suggestion and report back with the results. I will also try remaking it from scratch.
To answer your question, the media item got into FTM via Ancestry. I uploaded it some time ago, and it's been downloaded to FTM numerous times after unlinking andr redownloading the tree from Ancestry because of unresolvable synch failures.