Static resources are unavailable after some time

Question

I'm using Jetty v.9.2.10.v20150310, Spring 4.1.5.RELEASE.

I have configured the resources in Java:

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    super.addResourceHandlers(registry);
    registry.addResourceHandler("/static/**").addResourceLocations("/WEB-INF/static/").setCachePeriod(ServerVariables.getInstance().getCachePeriodForStaticContent());
}

It works fine for several days, beyond that the resources stop resolving. On the other hand all the paths, which resolve via controllers are stil working fine. There are no events or exceptions in the logs.

Any ideas?