Are you trying Syncovery version 6.18? If not please install that.
Is it copying three files in parallel? Maybe you can play with that setting, which is on the Files tab sheet when editing a profile in advanced mode.
Finally there are Advanced SSH Settings on the Internet dialog in the profile.
If problems remain, please send a complete log file to
support@syncovery.com. Try to cancel the job gracefully before sending the log file.