Hi,
I'm still investigating the issue so I could be wrong, but it's possible that since updating to 2016.0.0.0 from some 2014 version, SftpFileStream.Write has a bug that corrupt the destination file.
The created file has the correct length, but the content is the first 32.741 bytes of the buffer repeated till the correct file size is reached.
It's a pretty serious issue so I posted it as soon as I found out, I'm now investigating the issue in detail to confirm the problem.