You need to make sure Genre is Audiobooks–sounds like you are doing that. And make sure they are in the Audiobooks folder. The Podcast folder is treated slightly differently from the Music folder, which keeps it separate, but your problem is still with the tags since you are seeing Unknown.
Some tag–title?–must be missing or unreadable on the Unknowns. In Kid3, rewrite the title yourself and save it–don’t just accept what Overdrive provides.
And this is just a guess but…double-check your Kid3 settings (or options or whatever it’s called) to make sure the tags you are writing are ID3v2.3 ISO-8859-1 (there are various versions of ID3 tags and that’s the one Sansa likes). If they are ID3v2.4 the Sansa may not be able to read them. Newer books may have switched to ID3v2.4 .
