Article search on sub-topic is not working in esc pro

[KavyashreeR]

Has anyone come across a situation where article search is not working for a "sub-topic"?

On the same page, I was able to search for catalog items successfully, but articles are not being retrieved - even though they are mapped to the sub-topics.

Please note that searching under the parent topic works fine for both articles and catalog items. The issue occurs only when searching under sub-topics, and only articles are affected - catalog items are retrieved as expected. 

I also did full indexing for articles.. still no luck.
Kindly guide me on this issue..