When using Session Reliability, the ICA session does not reconnect after a disconnect while using NetScaler for ICA proxy.
With ICA proxy mode enabled, Session Reliability does not work for ICA session.
To resolve this issue update to NetScaler Gateway 10.5 build 54.9. This release supports the Session Reliability feature with AppFlow.
For more information refer to NetScaler Gateway 10.5 build 54.9 Release Notes.
2598 is the port used for application launch when Session Reliability is used. The AppFlow setting on the NetScaler prevents users to reconnect over port 2598.