I have a problem in navigation..

We have migrated from WebSphere Portal V5 to WebSphere Portal V6.0. The underlying application server is atV6.0.2.23.
Now In an cluster environment,we noticed In one of the Application server Left Navigation menu is disappear.
(this non-consistent behaviour is persist only for an hour/two) Then it start working fine..

we also identified, At the time of issue In home level the below code return false.

boolean nodeHasChildren = wpsNavModel.hasChildren(wpsNavNode);

There is no clear indication about any mi-configuration or wrong programming model.

Could any one Please help to fix issue

Thanks in advance,