When they restart, does the cont show that it is starting at 1 of however many?
or does the count show that it is restarting at some thing like 234 of however many?
One thing that may be happening is that it is only resending to 1 recipient.
it may that the email sends, then it fails on updating the record in the database that it has sent to that person. So when it restarts, it resends to that one person. If that is what is happening, I'm afraid there wont be a fix for that.