Jlpm build fails; vega5 extension

JupyterLab
1

Anaconda3\share\jupyter\lab\staging>jlpm build

returns

yarn run v1.15.2
$ webpack
C:\Users\Scott\Anaconda3\share\jupyter\lab\staging\node_modules\webpack-cli\bin\cli.js:93
                                throw err;
                                ^

Error: Cannot find module '@jupyterlab\vega5-extension\package.json'