The Buildr 1.4.8 ruby platform gem  seems to be present on the website and available through some API endpoints but not all. It is present in  but not . Note that gems of the same version but different platforms (java and x86-mswin32) are present in both  and . All gems were pushed at the same time.
The same problem seemed to occur with the 1.4.9 release of the same gem
The same issue with my gem https://rubygems.org/gems/couchbase/versions/1.2.0.z.beta5
But it isn't present in dependencies response, only previous version:
and it is responding with 500 error to http://rubygems.org/api/v1/dependencies.json?gems=couchbase
/api/v1/dependencies is provided by the rubygems/bundler-api project — perhaps you could open an issue over there instead? I'll look at this issue today, though. Thanks for reporting it!
I've just pushed passportist gem, I can see it through http://rubygems.org/gems/passportist, I can invoke gem install passportist, but I have no success trying install it with Bundler :(
gem install passportist
upd: an hour later it became OK
This was a bundler-api sync issue.
Temporarily avoid rubygems