I’ve never encountered this error before. This looks like an error coming directly from our storage provider, Google Cloud Storage. Butler implements uploads by generating a secure upload URL remotely, then sends it to your machine to upload the file directly to Google’s server for storage. (The file bytes skip our servers entirely to avoid any additional processing/slowdown).
This error suggests to me that something about the server you are running CI on is being restricted from accessing Google’s services.
Hope that helps