By "Your router" in Device Manager I take it you're talking about your network adapter? What are your power settings for the network adapter? Next time you have you device listed in Device Manager right-click / Properties / Power Management / uncheck: "Allow computer to turn off device" (or something like that). See if that helps.
You can download / save the
driver(s) for the network adapter anyplace on your computer and just point windows to the stored location when installing for the "unknown device". Don't need internet access for that.
Just wondering does this happen when you only cleaning the compute, doing something similar or is it totally random?