Technically this isn't a question, but a solution. I struggled with this problem myself for a couple hours, and saw other threads (now old and locked) that talked about it but didn't come to a satisfying conclusion, so I thought I'd post the solution I figured out. You need to disable "USB Selective Suspend" in your Windows power settings. For some reason the data being transmitted from Garmin Express to the GPS unit doesn't keep the USB connection awake if Selective Suspend is enabled.
Hopefully this helps someone. Admins, feel free to reuse the image for future questions of this type.
