It looks like there is a mismatch between the AWS classic load balancer timeout and the
org.atmosphere.websocket.maxIdleTime that results in
com.vaadin.server.communication.PushAtmosphereHandler - Exception in push connection errors.
The setting should be configured in the
web.xml as an init-param (stated in the JavaDoc in
org.atmosphere.cpr.ApplicationConfig) - is it possible to configure it in the application.properties of the Jmix project also?