I download the starter app from
https://vaadin.com/start/latest/java-ui
and run it inside Eclipse 4.8.0 on Tomcat 9.0.4 fine. (JDK 1.8.0_164 x64)
Then i switched to Production mode by 
selecting the maven profile productionMode (Ctrl+Alt+P)
and did Maven->Update Project…
after starting Tomcat again, I get the Exception:
SCHWERWIEGEND: Allocate exception for servlet [com.vaadin.flow.server.startup.ServletDeployer]
java.lang.IllegalArgumentException: Failed to find the bundle manifest file ‘frontend://vaadin-flow-bundle-manifest.json’ in the servlet context for ‘ES6’ browsers. If you are running a dev-mode servlet container in maven e.g. jetty:run change it to jetty:run-exploded. If you are not compiling frontend resources, include the ‘vaadin-maven-plugin’ in your build script. Otherwise, you can skip this error either by disabling production mode, or by setting the servlet parameter ‘original.frontend.resources=true’.
at com.vaadin.flow.server.startup.BundleFilterInitializer.readBundleManifest(BundleFilterInitializer.java:77)
at com.vaadin.flow.server.startup.BundleFilterInitializer.addBundleFilterForBrowser(BundleFilterInitializer.java:68)
at com.vaadin.flow.server.startup.BundleFilterInitializer.serviceInit(BundleFilterInitializer.java:62)
at com.vaadin.flow.server.VaadinService.lambda$init$0(VaadinService.java:258)
at java.util.Iterator.forEachRemaining(Iterator.java:116)
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580)
at com.vaadin.flow.server.VaadinService.init(VaadinService.java:258)
at com.vaadin.flow.server.VaadinServlet.createServletService(VaadinServlet.java:186)
at com.vaadin.flow.server.VaadinServlet.createServletService(VaadinServlet.java:167)
at com.vaadin.flow.server.VaadinServlet.init(VaadinServlet.java:71)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1174)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1090)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:770)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:133)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:417)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
This is the same exception I get for the application I wrote.
How to set-up production mode correctly?