sftp using proxy issue: ssh_dispatch_run_fatal: Connection to UNKNOWN port 65535: Connection corrupted

Our automated script connects to third party server (using proxy), to get some files over sftp. It usually works fine. On a random day, I got below error. What could be the root cause.? sftp> mget TR_ACK*.txt Bad packet length 1131376238. ssh_dispatch_run_fatal: Connection to UNKNOWN port 65535: Connection corrupted Connection closed Edit: FYI- Our script runs every 5min. The above issue occured at 12:05 min. The run at 12:00 min was also failed as the server was down at 12:00. The server was just up just before the time was 12:05 minutes.