Can you give us some examples? Screenshots would probably help.
One thing to keep in mind is that Roon has a genre hierarchy so, for example, Bop and Fusion are both considered sub-genres of Jazz. Changing your import settings determines what genres appear in Roon. This means if none of your file tags contain Fusion the genre won’t appear in Roon.
But if your file tags do contain both “Jazz” and “Bop”, Roon will still sort Bop as a subgenre of Jazz – the import settings don’t override the hierarchy, they just determine what appears in the list of genres.
Finally, note that the hierarchy can be edited by visiting the Genre’s page, and choosing Edit.
Hope that helps!