Events and Notifications app

I am looking at the output of the "Events and Notifications" app. It says there is a warning message, but there is no obvious way of finding it (the app should have a filter to only show errors, or only errors and warnings). I tried typing "warning" into the search box, and I saw loads of messages saying "Software repository configuration warning(s)".

Now I wonder what that means, and where to go to fix it. But there is no help in the app.

I tried searching all the log files for a similar message, but found nothing. What is the use of a warning tgat gives you no clue what to do about it?