I've create an application with JHipster v4. When I make a request on port 8080 it is returning a blank page. If I use yarn start, and I make a request to 9000 port, it is answering correctly.
Any idea?
By default, yarn listens on port 9000 (webpack + browser sync) to hot reload frontend code and contents, maven or gradle listens on port 8080 to hot reload server code. You must run both in dev.
If you start making changes to the client side code without having yarn start running, nothing will be reflected as the changes are not compiled so you need to either run yarn webpack:build manually after changes or have yarn start running.
It's written in the README.md of the project you generated and is documented on JHipster web site.