The dndConnector.js is not loaded and that's why the JS console is showing the errors. This can happen if the Production build of the Vaadin application is not included that JS resource as part of the packaging. Vaadin adds such resources if your Route annotated classes use those resources. However, it can not determine the required resources if something is constructed indirectly (for example, via Java reflection). In such cases, there are other means of informing Vaadin about it using @Use and @JsModule annotations.