I had the exact same problem as rdominelli, i.e. getting "Connection was lost" intermittently when sending files to a MoveIt server.
I upgraded to the latest version of SSH.NET but this caused the program to hang and then time out in Session.cs WaitHandle(), except it's not intermittent, i can reproduce the problem every time by making sure the FIRST file to transfer is approx 16K in size.
After some debugging i found that the problem is due to the initial server window size being 16K, and that the SFTP buffer size is set in SftpClient.cs SftpClient() to 16K so we get a situation only with the FIRST file, since after this transfer the window size is increased.
I reduced the buffer size to 8K and that fixed it.
I upgraded to the latest version of SSH.NET but this caused the program to hang and then time out in Session.cs WaitHandle(), except it's not intermittent, i can reproduce the problem every time by making sure the FIRST file to transfer is approx 16K in size.
After some debugging i found that the problem is due to the initial server window size being 16K, and that the SFTP buffer size is set in SftpClient.cs SftpClient() to 16K so we get a situation only with the FIRST file, since after this transfer the window size is increased.
I reduced the buffer size to 8K and that fixed it.