Application Cache Error event

Hello everybody.

I migrate company project from 7.1.15 to 7.2.0 and i get this error on client side (browser console):

Application Cache Error event: Manifest fetch failed (404) http://localhost:8080/package/VAADIN/widgetsets/com.{company}.{division}.{project}.{module}.ui.gwt.{widgetset}/safari.manifest
Failed to load resource: net::ERR_TIMED_OUT

Any suggestion how to resolve it?