Got it, thanks!
SELECTION_EMPTY error was triggered because the selection no longer matched any content after “Full” text was removed.
A simple solution is to include one more element from the page. In this case, include the page’s title "PHIL 120 Introduction to Critical Thinking" in the page as an additional element. Or, you can monitor the whole row in the table as shown below:
Once done, you should be able to get alerts when “Full” status is no longer present.
Hope this helps!