Second para. should read: "...happening; all "Arrange" options are disabled".
You should work with different layers and use a layer for page numbers (which should be on the master) on the top.
If this command is not available then it is because no other objects are below on the same layer on the same spread. If you see objects, they might come from the master.
Well, there are a couple of strange aspects to this: first of all, previously I have been able to send my image layers to the back for hundreds of iterations. Nevertheless, I'm happy to permanently move the page number layer to the top, to avoid that step.
However, in page master view I could not find an option to bring any layer to the top. It also appears that the page number and the page background are together in the same layer: when I try to delete the page number, the Background went away along with it. Believe I’m missing some fundamentals here?
FYI, I just went back to that image, brought it to the front, then got the "send to back” option, sent it to the back, and still the page numbers did not show up.
On any given layer, all document page objects are in front of all master page objects on that layer, so you must add a new layer to hold master objects, like page numbers, that need to be in front of background objects on your document page. Layers are arranged by dragging them in the layers panel.
Okay, on the master the page number layer is now on top. The image layer is not visible (like, it does not exist?) and page numbers are still not visible.
Running out of time on a publication deadline, will have to leave this for now, and may try to add the page numbers manually, later.
To give you any help we're going to need to actually see something. The master page with the layers panel open and all layers expanded would be a place to start, and the same for a document page (along with the pages panel visible and showing that page) for one that isn't showing what it should.
OK, will do my best prior to deadline, to finally get this right!