Hi,
Thank you very much for the details, I have logged in to check and test the issues.
I found the cause, the index table engine was not enabled on the search instance. I have enabled that for you: https://i.imgur.com/W5QrkKD.png
I also assumed you only want the post author ot be indexed, so I disabled these fields: https://i.imgur.com/SnQW7JT.png
The number of keywords can get higher as you expect, as the plugin does some processing and may create different variations for better matching.
It should return the expect results now.