This is a solution to an issue users have posted about a few years back with “ghosted” images when exporting a PDF.
If you export and the images seem to be in the PDF but quickly disappears after opening - try switching the order of the layers. For me, I had a PDF Title Block (exported from CAD) linked on the “On Every Page” Layer. When this layer was at the top of the list, I had the ghosting issue, presumably because a white mask within the PDF was covering the entire sheet that did not show when I was in Layout, only PDF exports. After moving this to the bottom of the Layers list, the images showed correctly after exporting.
Hope this helps!