LDN - Luminis Developer Network

We're running Luminis Platform 4.0.2.0 and have a timeout issue in Production, where, despite the setting below, if employees leave their browser sesion idle for about 20 minutes they get a 'Server Failed' of 'Session Expired' message:

configman -g session.employee.timeout
240

We've turned on DEBUG for the session.log and can see that eployees are correctly allocated a 4 hour timeout at login. We can even see them being timed out 4 hours later but, after 20 minutes or so, if they click on a tab, they are kicked out and nothing is dropped in the logs.