I don't see a difference between what works for me and what does not work for you. That leads me to think that it's an issue of file permissions. Make sure that the file on your site is accessible in a public manner. You may need to look at system logs to determine why the file is not seen by Roku. Otherwise, you may want to contact Roku Partner Success for their assistance.
FREE Windows desktop software for creating BIF (Trick Play), Direct Publisher (MRSS, JSON), and FireTV feeds @ GitHub/rrirower. No programming knowledge required.