Thanks - we’ve been able to see in your videos what you are talkin about, but we are still unable to reproduce despite several attempts on several different computers, OS’s, and networks. Your har file does not include any information about the downloads (working or not), unfortunately, so no more information was presented there.
What browser do you use? Maybe it doesn’t support multiple simultaneous downloads? Do other browsers show the same behavior on your computer? Your network is also very slow from that movie, so maybe it has bottlenecks, not sure. But I can download 2 of those simultaneously even with my network throttled down fairly far, and we do need to be able to see more than a picture of the problem to troubleshoot.