Well, that took waaaay longer than I'd hoped.
First problem turned out to be you were using the old (deprecated) Amazon S3 storage adapter, instead of the new "Amazon S3 (SDK)" one. The old one hasn't had any of the love the new one got last month - none of the thumb creation fixes. So the thumb path ended up being the same as the main upload path, and the thumb was overwriting the main image in S3.
Then it turned out you hadn't uploaded the most recent fixes for the new adapter, yours was missing a couple of critical fixes.
But even after switching your upload element to the new one, and uploading the latest and greatest, I had to track a new and interesting bug:
https://github.com/Fabrik/fabrik/commit/1d4b0e63ba4cc2ccf2cbb1669b1c48b8b9ff945a
... whereby if the main upload folder was specified with a trailing slash, like /uploads/s3/, and the thumbs wasn't, like /uploads/s3/thumbs, then the file path ended up being /uploads/s3/thumbsfile.png instead of /uploads/s3/thumbs/file.png.
Anyway, all fixed now. You now have thumbs and full size images, with lightbox effect in the list.
BTW - can you do me a favor and delete all my test files from your S3 bucket? I accidentally used some of my scanned medical records as test files, lol!
-- hugh