I just ran into the same problem, albeit in a different setup (dragonfly with S3 datastore). That seems to be the fogproblem.
Try using an older version fog. I updated mine Gemfileto use an older version fog.
gem 'fog', '1.4.0'
and then run
bundle install
I tried each version from 1.9.0 to 1.4.0, and 1.4.0 was the first version in which my downloads worked again. I am updating my post if I find a way to make this work with 1.9.0