When receiving an error like the following:
[ERROR] Failed transferring account "accountName" backup to destination "destinationName". Error: mux_client_request_session: session request failed: Session open refused by peer
Host key verification failed.
Your SSH destination may be hitting an SSH Multiplexing Limit.
This could be caused by remarking the MaxSessions at /etc/ssh/sshd_config on both your source server and destination and you may have set the 'Concurrent Backup Accounts' and 'Concurrent Restore/Download Accounts' values to 10 on the "Settings -> Performance"
As a workaround, please try disabling MaxSessions, restarting your "sshd" service, and lowering down the 'Concurrent Backup Accounts' and 'Concurrent Restore/Download Accounts' values to 5. Then we ask that you monitor your next backup job run, to see if this has addressed the issue.
