The initial message shows a successful connection:
[I 240305 12:51:12 transport:1871] Connected (version 2.0, client moxa_1.1)

but after that

getting this Error
site-packages\paramiko\transport.py", line 882, in get_remote_server_key
raise SSHException("No existing session")
paramiko.ssh_exception.SSHException: No existing session