Are you using Cloud Functions for event based processing ?

multiple_gcs_bucket_sensor.py

def poke(self, context):
        hook = GCSHook(
            gcp_conn_id=self.google_cloud_conn_id,
            delegate_to=self.delegate_to,
            impersonation_chain=self.impersonation_chain,
        )
        for bucket in self.buckets:
            match = [{'bucket': bucket, 'object': object} 
                     for object in hook.list(bucket)]
            self._matches.extend(match)
        return bool(self._matches)