Message logs in the Management Console of the cloud failover appliance (CFA) shows the following error:
backup.c:666 Network send error to SD. ERR=An existing connection was forcibly closed by the remote host.
This can happen when the Storage Daemon shuts down due to being killed by a process, which looks for out-of-space issues. It can also be due to a network connectivity problem in which the TCP stack on the CFA eventually closes the connection with a RESET.