Just so others that have the same issue with their ability to search in KBA on key words and stumble on this thread. Here is the outcome of the support ticket.
Within SmarterTrack there is a "NOISE LIST" any words in this list are ignored when performing searches. The list is hard coded and is unable to be updated or changed. "Words in the Noise list are excluded from being indexed. That is why they return no results in the search"
So unfortunately until this is exposed so that you can control the "Noise List" in SmarterTrack users will not be able to find key articles if they are searching on words that someone at some point thought would be good to exclude from the indexing process and hard code them in the back end where you can not get to them.
Hopefully a future release? will expose this list so you can adjust it to make the search function in the KBA area effective when searching for words that are relevant to your organisation.
Hopefully if you have the same problem your search will find this thread and is not lost in the hard coded noise list and save you some frustration and time wondering why.