The "Google Cloud Storage Upload Report" view for a build currently uses https://storage.googleapis.com/[BUCKET_NAME]/[OBJECT_NAME] for the download URL. This works for publicly readable storage objects, but not for ones using access control. The correct URL is https://storage.cloud.google.com/[BUCKET_NAME]/[OBJECT_NAME].

This is documented here: https://cloud.google.com/storage/docs/collaboration