It is not unusual to get different results when changing USB ports.
Remember this. No matter how many USB ports are available on your computer, the chances are, there are only two hubs supporting all those ports. It is quite easy to overload one hub and not even touch the other hub.
I wish computer manufacturers would identify the hubs for each port (i.e. Port/Hub: 1/1, 2/1, 3/2, 4/2...)