Hello.
If you currently are duplicating to 2 servers and you shut down the primary one, device would still try sending records to both servers the working one and not working one. It is recommended to remove inactive server from configuration, so that device would not be attempting to constantly send to deactivated server as in such case it would be storing records on internal memory as it cannot send them.
So it is highly recommended to adjust your configuration as needed if one of the 2 servers device is sending to get shut down.
Best Regards