I was persistently getting the error:
Bundler gave the error "Could not find json-1.8.1 in any of the sources" while processing "/Users/tpowell/projects/some_other_project/Gemfile". Perhaps you forgot to run "bundle install"?
It is recommended to not use the rbenv-bundler plugin, as it has been the source of many problems
I ended up uninstalling the rbenv-bundler plugin as a result.
But hey, kudos to rbenv-bundler author for taking the complaint in stride.