Tree Performance Issue

Hello - We have a very strange Intermittent issue with custom trees, there are couple of nodes under that tree which we are not able to expand, when we click on expand node, system keeps on trying to expand and than finally page sign out but some time system allows us to expand the same node, we are trying to find out when system does not allow and when system allow to expand the same node.

Some times when we save the tree and another name or effdt, it allows to expand the node but after some time again we start getting same issue, some times by clearing the cache helps.