I really appreciate your reply - sorry for my super-delayed response! I've been busy these past few months finishing up my thesis and defending it.
I did try to reinstall the drivers, but it seemed that they were all up-to-date, so reinstalling didn't change anything. Ultimately I think it was a hardware issue: I think water had spilled out of a container on the balance at some point and gotten into the pinned connector cable that linked the balance to the computer. When I disconnected the cable, the terminals looked corroded beyond recovery. :/ Oh well.