In the case where PCE calculates a path with "include nodes" type constraints, and that GNPy does not validate the selected path, if GNPy finds another suitable path, it proposes to PCE the new path under the form of new "include nodes" constraints, which this time contain the full path to select.
However, in PostAlgoPathValidator, PCE verifies that the calculated path includes the nodes regardless of the order of the nodes. Also, if there are multiple paths passing through the same nodes, but in a different order, PCE may select the wrong path.