When setting gradle-home-cache-cleanup: true, the action will attempt to remove all unused files from Gradle User Home before saving the state.
When running a build with state loaded from the configuration-cache, many files in Gradle User Home (eg dependency jars) are not necessarily recorded as being used during the build.

Taken together, this means that after a successful build with configuration-cache reuse, the saved Gradle User Home will have no dependencies. This can result in a ClassNotFoundException failure in subsequent builds.