Fixing Name Resolution in Ubuntu 18.04

We have a server (really a powerful workstation) running Ubuntu Linux that sits in the corner of a professor’s office which we use for teaching the Modelling Materials course. It had been on Ubuntu 16.04 since we installed it last year, but I upgraded it to 18.04 about a month ago ahead of the start of term. Everything worked fine, except for one pretty annoying thing: it quickly became clear that primary group names weren’t resolving.