Category hierarchy lost

Upon upgrading to this version I have found that category hierarchy is not displaying on the FAQ page. Only the lowest level categories are showing.

The page used to be collapsed under top categories like this:
Top Category 1
- Sub Category 1
-- Question 1
- Sub Category 2
-- Question 1
-- Question 2
Top Category 2
- Sub Category 1
-- Question 1 ....

But now the Top Categories don't appear. When you click on the question you can see the breadcrumb is still correct - i.e. the taxonomy hierarchy is still there, it's just not displaying on the FAQ page.

My categories settings are 'Clicking on category opens/hides questions and answers under category'. I have verified that the FAQ content type is still enabled for the FAQ taxonomy. Thanks.