Bundler reports errors across several different projects when running `bundle install`

When running bundle install, I was getting the following for several projects:

Bundler gave the error "Could not find {gem_name_version} in any of the sources" while processing "{project_path}/Gemfile". Perhaps you forgot to run "bundle install"?
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I found someone else was having the same problem too.

In my case, I had uninstalled and reinstalled a version of ruby using rbenv and began seeing this error reported for every project using the same ruby version as the one I had uninstalled and reinstalled. I haven't exactly gotten to the bottom of why this happens, but going around and running bundle install in each of the project directories got rid of the error.