Well, that setting is also available in menu items (like category blog) and each individual article. So make sure that it has not been modified somewhere else.
Note that if your articles show under a specific menu item, you should check that menu item.
I found the solution. Although I had set global options to SHOW and I had set Show Intro Text to: Use Global (Show) - I had to change to SHOW. I may have created the articles before I had set the options.
Thanks for your help!
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