Hey!
Since your other switches can backup normally, the SFTP server should be no problem.
Please check the following items:
1. the link between eSight and the switch;
2. the configuration on the switch.
a) Check whether the VPN instance is required for logging in to eSight through FTP (the set net-manager vpn-instance command configures the default VPN instance that the NMS uses on the device).
b) Check whether the first-time authentication is enabled on the SSH client (ssh client first-time enable)
c) If the source IP restriction is imposed on eSight, you may need to run the sftp client-source –a command to specify the source address of the packets sent by the SFTP client.