Problem With Move To S3

From time to time, I get a really annoying issue when I attempt to move images to S3. I cover reasonably large events which yield a two to three thousand images a day, which I upload directly to my server. Once they've all been processed by Sytist, I then click the Move to S3 button.

Sometimes all works as it should, I get the little orange bar pinging backwards and forwards at the top of the screen and the images tick themselves off the list. Other days, it'll start out as it should, but will quickly stop working. The orange bar flicks very, very quickly but there's no other screen update. I've left it in this state for a while, but it doesn't appear to be moving the images.

If I stop the move and start it again, it'll move a few over and then flake out again.

Any ideas what I can do to resolve the issue?

Kind regards

Simon

Sounds like either a network issue between the server and S3 or perhaps it is triggering something like mod security on the server and it is just returning 403 errors. If you can pull up the network console in your browser you may be able to see if you are getting 403 or 500 errors.

"The orange bar flicks very, very quickly but there's no other screen update. I've left it in this state for a while, but it doesn't appear to be moving the images." 

It does to me too, but checking into s3 the process is going on.  When the transfer is finished, the fast flashing strip on sityst disappears, it does this to me