Well now, when I start to Export my book cover to my desktop, solve my Preflight Verifier issues (not so fast), select export, and then select pdf. A dialog box pops open and (as an aside) identifies my "current file" as Postscript, I assume having been automatically assigned since I did nothing to the contrary. I'm offered several flavors of pdf-, none of which are the pdf-x-1a I am told, in this case by Ingram/Spark, that is required. To be clear I suspect that this is probably a distinction that will be solvable after the mess I'm in at the moment is caught up. (I did finally solve this one later via Google.)
I choose one of the pdf's offered other than pdf-x-1a, since I'm only saving to my own desktop and click Export. The export shows up on the desktop as an .sla. That is where the first horror begins (please know that I've spent hours on Google and reading the manual before posting this).
When I completed the export, my book cover looks fine (see screen shot). Please note, and it might be important, all the inserted frames are outlined in a pale red. All is well it seems and so to organize my desktop a little I put the image, that I had imported on to my desktop as a .tiff, into one of OS X 10.11.6's folder icons. It was then inside this little folder and not visible as a file icon on the desktop.
At some point I re-opened the saved desktop export and was confronted with this (see second screen shot). Initially the opened export has only the bright red X with the imported image name "mountain.tiff" in a stark white box in the middle with the frames shown in pale pale orange. No amount of clicks changes anything except the locations of the bright red handle frame.
I pulled the image out of the little folder icon back onto the desktop as its own file icon and by its presence as such, it repopulates into the image box, sometimes I click something but randomly it seems to reappear in the book cover again on its own. I save and close the whole file to my desktop again and reopen it, voila, the image is there again. All seems right with the world--so long as the image, "mountain.tiff" sits as a file icon on my desktop--not (hidden) inside a folder icon. One additional note, while the book cover looked fine again and was--open, I took the image file on the desktop and put it back into the folder while the book cover was still sitting open on my desk, the image disappeared from the book cover as I watched--without closing.
Needless to say, I think something will be terribly wrong if I send this file out into the mean and expensive printer-world that doesn't know the image is visible on my desktop, not in a folder thereon. If it helps, the Preflight Verifier now shows: " Image3 Missing Image (black square) Background", however this time I know what the problem is. If it might be important, I note that the properties window shows the image named as "mountain.tiff" not as "Image3". My route for getting the image was File > Import > Get Image and selecting "mountain.tiff" while it sat on the desktop.
I had a random thought when reloading the image for the millionth time that maybe at > Get Image, I should try choosing the desktop folder icon and opening that to choose the image from inside it rather than from its own file icon dragged to the desktop. And damn, after two days and making you read this day-long composed post, I think I solved my own problem. After about six openings and closings the book cover opens just fine, no image disappearance. And no "mountain.tiff" icon visible on my desktop. I hope this tale is helpful to you or other users.
But wait! That isn't the end of it. I sail through Preflight Verifier now, it doesn't even pop up, and go directly to the final export Save page. Everything seems fine and so I hit save. This is what arrives on my desktop (see third screen shot). The image arrives but no text (compare screen shots). Please note from the first screen shot the Text Frames are outlined in pale red, sometimes these outlines have been in pale brown before exporting, but I don't what I might have done to cause that or not cause that or if it matters. If it does matter at one time the frames showed up in the text color (CMYK Orange 3) but no text inside them. I have no idea what caused that.
The font is Baskerville Regular chosen within Scribus and doesn't seem to have any of the "embedding" issues I've seen via Google. The Properties palette > text doesn't seem to bark about it in anyway, I can't seem to find any print "lockout" issues, and I have only one layer that everything resides on, the text frames added last.
I'm worn out, can anybody help me on this?