Recently, we've been having some issues with code reviews on the reviewboard instance I set up. Petr was not able to create a review for a fedora-build-service patch and a review I set up is showing diff errors.
I started digging into this yesterday, and it turns out to be a problem with the fedorahosted cgit instance that reviewboard uses to get files to generate the diffs - it's not returning the right file contents. In some cases, it returns blank files. In other cases, it returns 404 errors (what petr was hitting) or HEAD from MASTER instead of the file requested (what I was hitting).
After talking with nirik in #fedora-admin, it looks like this might be an issue with the fedorahosted.org setup of cgit because while I can reproduce the issue on freedesktop.org's cgit instance (which is probably using the same redirects), I can't reproduce the problem on the upstream cgit instance [1].
[1] http://git.zx2c4.com/cgit/
I've filed an issue with infra [2] and will update this thread when we know more. However, until this is resolved - code reviews on reviewboard aren't likely to work 100%.
[2] https://fedorahosted.org/fedora-infrastructure/ticket/3687
Tim