Vaadin Session Timeouts happening before the session timeout

Good Morning,
I'm running into an issue where the session is timing out anywhere between 5 and 20 minutes.  This is happening very sparatically.  About half the time, the session is timing out at 90 minutes (from web.xml).  After thinking that the heartbeat could've caused this, I disabled the heartbeat and received the same results.  Have anyone else experienced this?

My web.xml currently contains the following:
<init-param><description>Enable Session Timeout</description><param-name>closeIdleSessions</param-name><param-value>true</param-value></init-param>
<session-config> <session-timeout>90</session-timeout> </session-config> <context-param> <param-name>heartbeatInterval</param-name> <param-value>-1</param-value> </context-param>

The configuration that we're using is VAADIN 7.7.3/Tomcat 8.0.41.  I have the application setup for Long Polling.  I searched through the log files and there are no issues being reported.

Any help would be greatly appreciated.

Thanks,
-Jeff
 

This was an issue with load balancing rather than Vaadin.  This has been fixed and the application session timeouts are now active.