The dashboard report shows zero pages in en.WP, but there are 23 pages with errors. They are in a subcategory. The report may need to traverse subcategories.
Topic on Talk:Parsing/Replacing Tidy
I intentionally didn't traverse subcategories, because if "Category:Foo" has a improperly closed tag in it, then it will appear as a subcategory to the main one, but the articles inside that subcategory are totally fine.
Can you parse the system message with category names, retrieving only relevant subcategories, Legoktm?