A RubyGems repository that is marked as offline will respond with a 500 to certain requests. This will make packages inaccessible to bundler requests.
Notice the call that fails:
1. Create a remote RubyGems repository
2. Create a GemFile with a few dependencies, such as this:
3. Use bundler to pull the dependencies: bundle install --no-cache
4. Set the repository as offline
5. Remove the gem files (rm -rf vendor)
6. Attempt the bundler pull again, notice failure.