Retention Policy Issue
Currently, there is an issue when connecting to a Google Cloud Bucket that has an active retention policy.
When you use the Test Connection feature on the Cloud Connection pointing towards the bucket you will receive a negative result for the write permission.
The reason you receive a negative for the write permission is because the server is unable to modify and delete the test file it sends to the bucket during the Test Connection. Since the Test Connection needs to be able to write, modify and delete an object from the bucket, it will fail the write test since it can't modify or delete the object.
Another reason why a retention policy can cause an issue is when the server writes data to the bucket, it first writes a 0 byte file as a placeholder for which it will stream the data into, which would be an overwrite event. So, for however long the retention policy is, is however long the server is unable to populate the 0 byte file with the correct data, since it can't overwrite it due to the policy on the bucket.