Hi @davecj,
The actual error in your log is this:
Failed to load plugin: properties failed to load for node-red: Additional properties are not allowed ('npm-flags', 'node-engine', 'node-packages' were unexpected)
See https://snapcraft.io/docs/nodejs-plugin for updated documentation of the plugin. The above properties are deprecated, and assuming your project has a package.json file, you should do away with node-packages and npm-flags, and node-engine should be replaced by nodejs-version.
Hope this helps!