@eromano, I tried to install OpenWRT on a VMWare VM for a while. I got version 15 installed using an OVA but I couldn't get openssl working, so I couldn't install nodejs etc on it.
Anyway, I noticed your error output shows it's trying to access a URI that starts with /engine.io . That's not valid URI.
I wonder if you've upgraded socket.io-client beyond the version specified in ubuntupackage.json because this article says the latest version 'socket.io-client@4.X.X uses /engine.io instead of the valid /socket.io URI.