A Session switches the Management Unit on its Uprocs via a HDP, like for example: {A } or {S } and is working fine switching the execution Node as pointed by the Management Unit Dependencies of the MUs A* with S* and viceversa.
After an unknown event or modification occurred at a specific date, the session stops execution in one of the nodes and does not continue to execute in the node where the Depending Management Unit points.
How to find out what the problem is and to fix it?
Missing MU Dependencies on the involved Management Units on both Nodes.
Release : 6.x
Component : DOLLAR UNIVERSE
In order to find out what the problem could be, the first thing to do is consulting the Audit Trail of both Dollar Universe Nodes, looking for any modifications performed around the day that the Session stopped working as expected, filtering on Object Type:
MU, MU Dependence, Session
In this case, we would find that a necessary MU Dependency had been removed that day, so recreate the necessary MU Depencies on both nodes to fix the problem, but a modification on the Session or MU could also produce a similar problem.
As a golden rule, please always verify that Object Definitions ( Sessions, Uprocs, MU Dependencies, MUs ) are coherent on both Nodes.