Example repro using a lit based web component

in development mode npm start everything works fine. when building npm run build -- --prod and serving, the web component code is missing

Solved: The problem turned out to be @angular-devkit/build-optimizer assuming all decorators are side effect free (which lit's isn't, and, assuming neither is Stencil's). See this discussion angular/angular-cli#20714 (comment)

Registering the lit component directly (e.g. customElements.define('simple-component', SimpleComponent);) works.