OK, atm I do not have any other idea, what to try.
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
And do you have a reason to believe that you can get more than 40 Mbits/sec? Do get more in any other FTP client?
Win7 built-in FTP: 105 Mbits/sec
Filezilla: 60 Mbits/sec
WinSCP FTP: 40 Mbits/sec