I have a theory. I am not sure how to test as that depends on the source of the issue. I noticed that in the branch below, the lowest level are duplicated. Now, when it comes to the Part Classification facet, only the leaf nodes are displayed. This presents a problem for the code as it now has two different nodes with the exact same name. You can see below my attempt to alter the Military Zener category to no immediate effect. I observed that when I asked to see all Diodes and then looked at the facet, I saw only one listed for each display name and its counterpart was displayed as an internal name. There seems to be a if/then/else rule in place but not sure if this is Windchill or SOLR as the source. I should be able to vary the node display names slightly to avoid this situation but would like to know how best to correct if I see it in production.
