Answer:
A page that gets a Didn't Load flag
Pages with an obvious problem with functionality or errors in displaying content
Explanation:
The main reason why a page gets Page Quality rating Low/Lowest is if it can't be shown for one reason or another.
A page with mismatch between the location of the page and the rating location, does have a mismatch but some form of a page is shown.
A file type other than a webpage displays that specific file type in a page framework, so page is shown
Other two do not show a page, so they will get a PQ rating Low/Lowest
