Session expires randomly

Hi everybody,

we have a serious problem: the vaadin session randomly expires.

We get this output from tomcat logs when this happens:

mar 19, 2018 12:25:34 PM org.atmosphere.cpr.DefaultBroadcaster addAtmosphereResource
AVVERTENZA: Duplicate resource d7334a21-db0d-47d4-bd6a-c40abf32608e. Could be caused by a dead connection not detected by your server. Replacing the old one with the fresh one
mar 19, 2018 12:26:11 PM com.vaadin.server.ConnectorResourceHandler error
AVVERTENZA: Ignoring connector request for no-existent connector 1070 in root 0

We can’t track the source of this problem.

We are using latest production Vaadin 8 version.

Any suggestions?

We deploy our application with tomcat 9 + nginx proxy