The following ISBNs were run through the metadata wrangler. They have full-size cover images, and they have URLs to cover thumbnails, but the actual thumbnails are missing.

It's not clear whether the thumbnails couldn't be generated, were generated but couldn't be uploaded, or if there was some other problem. It's also not clear whether this was caused by a bug in the code, a problem with the image files, a temporary network failure, or a misconfiguration of the metadata wrangler.

9781250112293
9780307530646
9781633758483
9780385374804
9780375894527
9780307771544
9780307771483
9780307978820
9781101099636
9780375895722
9780375898822
9780375987380
9780307779878
9781101640036
9780375980084
9780449811412
9781101620960
9780375981340
9780385372800
9780385374682
9780385374736
9780385374620
9780385374750
9780807007471
9780385374811
9781250155627
9781633753877
9781466895140
9781627793223
9781466896123
9781101171127
9780307560674
9780375983443
9780385374507