Removing redundant tasks

Good day!
If a problem in the transmission queue come from the scheduler, and the scheduler is triggered, for example, when you change a file, and at this time there is no access to a remote server, then the queue gets a lot of the same tasks.

The problem in general consists of the following:
There are several dozens of remote FTP server to which every hour should be laid out "fresh" files (both from remote servers out the file and this problem also multiplied)
The problem is that due to the technical conditions of these FTP servers are not routinely available and are reproduced to a regular task list, and as a result, these tasks are performed repeatedly, which affects the volume of the traffic.

Is it possible for any of the stages (or the scheduler queue, etc.) to control the list of tasks for identity and delete duplicate.

There is a setting to force serial execution of the "tasks". Other than that, duplicate tasks cannot be automatically removed. But generally if the file already exists, then the transfer will be skipped.