The planets on the large size of the gap are not gas giants, so that cannot explain it.

Do you have more information on that? "Hot jupiters" are close in gas planets and the should appear at low semi-major axis, above the Fulton gap. (Disclaimer: I am not a planetary scientist, but my office mate is and I learned just enough to be annoying)

Sorry, I don't have any further insight, as my reply was based on information from the posted story.