For some reason, on this content-type which has the value of "SL Document" set as their parent in my content hub, it shows up like this in my Document Library content-type settings:
If I then click on that parent link, it reloads into a page called "Site Content Types : Site Content-Type ", and the correct parent content-type of SL Document is listed.
Throughout all of this, my parent content-type's metadata column of "Classification" is missing in the document library. I have republished the parent a few times now, waited a day, and the "Classification" column is not coming through. In the screenshot, you can see that the column from the parent called "Keywords" (multi line type) is coming through. I am out of ideas here, and Microsoft Support has been looking into this for weeks now without any progress. All help is appreciated!