Can you please confirm with the new MediaAgent, is this a Local MediaAgent or a Cloud MediaAgent?
Also while running Aux Copy to the Cloud Library, is this going through the new MediaAgent to the Cloud MediaAgent or directly writing to the Cloud Library ?
At the moment I would recommend using the CloudTestTool to just test the general connectivity between MediaAgent and Cloud, and see if there are any latency that could result in "Unable to setup the copy pipeline"
In most case when Commvault reports "Unable to setup the copy pipeline", this is an indication that the initial pipeline established between the Commvault MediaAgent and the Cloud Library for write process has been interrupted, which could be a result of various factor (i.e. environment, process crash, timeouts, latency and etc).
But to narrow it further it is recommended to rule out factors such as environmental (connectivity), by testing the upload/download speed between MediaAgent and Cloud
Link - http://documentation.commvault.com/commvault/v11/article?p=9228.htm
If you can give the above a go and share the results that would be great.