When a session is stored in HADB, it includes some time information, including the last time the session was accessed and the last time it was modified. If the clocks are not synchronized, then when an instance fails and another instance takes over (on another machine), that instance may think the session was expired when it was not, or worse yet, that the session was last accessed in the future!
In a non-colocated configuration, it is important to synchronize the clocks on that machines that are hosting HADB nodes. For more information, see the Installation Guide chapter, “Preparing for HADB Setup.”
Verify that clocks are synchronized for all systems in the cluster.