Vaadin 14.1.3 Blank Page, get client.cache.js aborted 404


my Vaadin program starts without problems and all sources are build (e.g. generated-flow-imports.js). I got no java compile error or runtime error.
BUT i only see a blank page in browser and the console shows following error:
GET http://localhost:8080/MyProgram/VAADIN/static/client/client-FCCC15DDC39AFA7323E81DFDEFA160A8.cache.js net::ERR_ABORTED 404

The program runs on a Tomcat 9.
Did someone have the same problem or know how to fix it?