Is there anything helpful in the discussion at this weblink? Maybe the problem you describe here is not restricted to the SanDisk Clip Sport?
http://www.applevis.com/forum/ios-ios-app-discussion/known-problem-certain-audible-books-and-apple-devices
“All Audible books longer than a certain time, something like 24 hours in Enhanced format will have this problem. Apple and audible are aware of the problem and Apple seems to have no real interest in fixing it. Audible suggests that one set the Audible library page to split the book up into sections”
