The buildpacks only support the most recent two versions of the installed dependencies. The applications that are configured to use a fixed dependency eventually run into issues as a buildpack is upgraded. They include newer dependency versions and drop the dependency version required by the applications.
Examples:
Affected users see an error message like this:
Could not get translated url, exited with: DEPENDENCY_MISSING_IN_MANIFEST: https://path/to/ruby-2.1.0.tgz
If an application depends on a binary dependency which is no longer supported: