The generic image is intended to be a placeholder while media is transferring. If the media has all been processed, and there are no errors to deal with, then if the generic image is still there, it's because the sync broke. Unfortunately, that's still happening to a lot of us.
Please document what you're seeing with screenshots and attach them to an email to firstname.lastname@example.org
with the request that they be forwarded onto the developers.
Once you've done that, you've got to manually fix all the stuff that didn't transfer. Unfortunately, that essentially means deleting each instance and putting it back onto the tree.