Automated FTP transfer from mapped network drive

My use case is I have a group of users who prepare documents that get sent to a government org over sftp.

The way we have it setup is that the users have a mapped network drive to a share on a Windows server. On that server we have an in-house built windows service that watches this directory for folders and then uploads them to the FTP with all their contents. The folder that the users copy will have a number of documents.

It seems to work most of the time but I don't know we are being told from the government org that sometimes files are missing from the folders. I think our in-house solution must not handle some race condition or something correctly. It tries to check if the folder is still being written to before initiating the copy.

I would like to move to something commercial. Anything out there you can recommend?