I was copying large files (2GB+) from a Windows 10 desktop to a linux system using WinSCP 6.2.1 with no problems. Today, I upgraded to 6.3 and then each time after the copy completes I would get an SFTP error 5 that it couldn't rename the file from xxxxx.yyy.filepart to the actual filename (xxxxx.yyy). If I tried to manually rename the file on the remote Linux system in the Interface (right-click Rename), the same error would show. After multiple attempts with different files and always the same result, I decided to revert to the previous version 6.2.1. After uninstalling 6.3 and reinstalling 6.2.1, the copy worked as expected without any errors. Looks like something got broken in the newer version. Below is a copy of the error text that was appearing. I don't want to spend any more time on the issue, already lost enough time as it is. Just posting this as a courtesy to help others or the developers.
Bad message (badly formatted packet or protocol incompatibility).
Error code: 5
Error message from server (en): badly encoded SFTP packet