Hello,
In order to run kibana in dev mode, you need to specify the --dev flag to the Kibana CLI while running it.
You can tell Kibana is running in dev mode if you have the kibana.dev.yml file present.
There are potential problems when running Kibana in dev mode, as it's noted in the Contributing guide ( https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md ) :
In development mode, Kibana runs a customized version of Webpack with some optimizations enabled to make building the browser bundles as fast as possible. These optimizations make the build process about 2x as fast for initial builds, and about 7x faster for rebuilds, but are labeled "unsafe" by Webpack because they can sometimes cause changes to go unnoticed by the compiler.