Hello,
Thank you for bringing this to our attention.
I am currently investigating the issue.
One thing that you can try is to set the TCP/IP buffer size to (default)
Main menu > Options > Preferences Dialog > Connection
Set the TCP/IP buffer size for send and receive to default
See
this faq entry for a screenshot.
Connect to the FTP server and try to upload the files.
Also please upgrade to v4.4.2 build 2018
You can perform a manual update check from within FlashFXP via the main menu > Help > Check for new version.