I'd facing the same issue "Server signature is not valid." when attempt to connect to sftp with version 220.127.116.11.
I'd tried with the property PreferredHostKeyAlgorithm for all values, it return same error "Server signature is not valid".
How to resolve this?
However, I also tried with using Rebex Sftp component 5.0.7501.0, no problem for connection and login.