In the past, with Volumio 2, I blindly used the following;
npm install socket.io-client@^1.7.4
to install the node modules needed for my plugin.
While updating the plugin for Volume 3 I’m noticing occasional errors and timing problems. Should I be using an updated version? If so, which?
Many thanks in advance for any help!
Still the same old one 
If you want to avoid multiple copies on the local device, you can always do:
const io = require('/volumio/node_modules/socket.io-client');
const socket = io.connect('http://localhost:3000');
That way you don’t have to install multiple copies of the same module.