Thanks for the reply! While browsing the documentation, I found a section in the Xcalar documentation where there's a section called: "Understanding log messages" - see:
After playing with it based on this document, I found that there are two modes: the "get recent logs" mode, and a streaming mode (which is entered if I click on the "Start Monitor Stream" button). These modes are mutually exclusive - so if I am in the streaming mode, latest logs are posted in the window, and keep rolling up as new logs are generated, whereas the "get recent logs" just gets the latest logs one time. If I am in the streaming mode, entering a number in the get recent logs window doesn't do anything or disallows me from entering a number - until I quit the streaming mode by clicking on "Stop Stream".
So maybe I was in the streaming mode, when I posted this question...which disallowed me from entering the number in the "get recent logs" window. Maybe the panel could be made more intuitive (e.g. when I enter the number in the "get recent logs" button, it could warn me that I am in streaming mode...).