I took a look at your updated feed and was able to view a video in a browser, so, I'll assume your files are public. I've seen this problem before but can't quite remember what causes it. A couple things to try... Rename your feed file and upload it again. Feed updates are not immediate if you use the same name and are using CloudFront. The caching gets in the way at times. If that fails, turn on the S3 logging for more info on the problem.
On a side note, I am developing the second release of a software product that can read an Amazon feed and convert it to Roku. I've also got another product that converts from Roku to Amazon.
FREE Windows desktop software for converting Direct Publisher channels to SceneGraph (SDK), for creating
BIF (Trick Play) files,
Roku (MRSS, JSON) feed files, and
FireTV feed files @
GitHub/rrirower.