I think the comments above, regarding the sleep command is required, and so is the file check logic after the loop.

Suggestion 3.

The script putting the file onto the server should copy to a separate folder and after the copy completes, should use a 'rename' command run on the target server to 'move' the file into the target folder after file copy.

It is unlikely for a Rename command to be swapped out during execution, when ssis goes to pickup the file it will be completely written.