I fixed this problem for myself by locking wifi on using the wifi locker and going into the nooklibrary app and refreshing from B&N source in the app.
It is important you have an open connection to get the cover art reliably, at least for me and the old version of nooklibrary I am running (0.9). I have had similar issues with the B&N library as well so it is not unique to the nookdevs code.
-Duncan
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