David, notice that any of your searches where 'city' is not at the end are the ones where it fails to find any images. This is because city is a built-in alias to search for any of the 3 columns that can contain data about the city.
Using any of the words in the "Field name or Alias" column of the "Searchable fields" page could potentially cause an issue. For example, entering "stop city police" (without quotes) is going to look in the city field for the world 'police'.
To get around this issue surround the word city in double quotes for the search queries you listed that return no results, for example, stop the "city" police protest.