APM+LTM -> VDI iAPP

I currently deployed the Citrix VDI f5.citrix_vdi.v2.1.0 where the APM is reverse proxying traffic to the storefront gateways. After 20 minutes, the Storefront idle timeout disconnects the session. You can tell the APM to still keep the session, but then this keeps sessions open and can have potential session issues in APM. How come the keepalive from Citrix Storefront is not properly passing through the APM? If I go directly to the Storefront, it works fine.