After you upgrade to version 4.7.0, maybe you will get such error "Failed to exchange the keys", because the version 4.7.0 changes the ssh host key into the PEM format, so if clients use Linux command "sftp" or sftp software based on OpenSSH, they will get a warning says the fingerprint for the host that was previously stored no longer matches the target, there are two methods to solve such issue under the client side:
1. Modify the file "~/.ssh/known_hosts" (or "C:/Users/YourName/.ssh/known_hosts" under Windows), delete the line containing the hostname of the server you’re trying to connect to.
2. Or just remove the file "~/.ssh/known_hosts" (or "C:/Users/YourName/.ssh/known_hosts" under Windows).
3. Either remove host fingerprint: ssh-keygen -R ServerName
P.S. since version 4.7.6, we provided a tool for converting the old PKCS#15 ssh key to the PEM format: viewtopic.php?f=2&t=3257