Sounds like it may be a software issue. Computer based player software often has settings that can be adjusted. For example, you may have a replay gain or other setting enabled on the computer that is affecting volume or other adjustments.
There could also be other issues (say with the USB interface, etc.) but I'd start by carefully going through every software setting you can find.
There could also be other issues (say with the USB interface, etc.) but I'd start by carefully going through every software setting you can find.