Thank you for the log. It seems that there is only one request running parallel to the progress request. Could you try, just for the sake of trying, to stop the other request while there is upload monitor in progress. I mean the Common/ServiceProxy.aspx. It looks like that there is another async XmlHttpRequest constantly polling to the server, in parallel with the other two requests (the fist one containing the file being uploaded and the second is the progress polling). I believe that this might be the reason for the problem.
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