A simple Google search on “Focusrite Scarlett disconnect” reveals this to be a common problem with no clear solution. I’ve experienced and solved this issue on two independent PC+Scarlett setups, and both times it boiled down to the same problem: the USB cable.
Not only do you need an A-to-B cable specifically rated for USB 2.0 (or higher) compatibility, but you need to ensure it is a short cable (I’d say 6 feet max) with at least one good ferrite core around the end that plugs into the back of the Scarlett. Ideally you’d use a cable with two ferrite cores (one around each end). And do not use a USB extension cable or USB hub in between the Scarlett and the computer.
In case you don’t know what I’m talking about when I say “ferrite core”, just plug the following search into Amazon: “USB 2.0 A to B ferrite”.