Another idea occurs to me. As a sort of Backlight life-hack, you could create an album or album set to be used as a page – hide it from indexing, add it to your navigation – and then add an image as for any other album.
Thanks, Matthew and othrs. This is certainly curious, and now, the album has decided to show itself again. I can live with that, since the whole thing seems to have taken on a life of its own. In Lightroom, I can change the order of the images which I shall now do.
A dear friend once used the phrase “the perspicacity of inanimate objects” to mean, these things have a mind of their own sometimes!