You started the application from an IDE and you didn't run npm start or npm run webpack:build.
You had a network error while running npm install. If you are
behind a corporate proxy, it is likely that this error was caused by your proxy. Have a look at
the JHipster error logs, you will probably have the cause of the error.
You installed a Node.js version that doesn't work with JHipster: please use an LTS (long-term
support) version, as it's the only version we support.
Building the client side code again
If you want to go fast, run to build and run everything.
If you want to have more control, so you can debug your issue more easily, you should follow the
Install npm dependencies with the command npm install
Build the client with the command npm run webpack:build or npm start