Categories have disappeared

I updated to 3.4 a few days ago and things have been buggy. But I haven’t found workaround to my latest problem. All of my category “pages” that are in my menu at the top of my pages are either coming up with a 404 or one article that is in that category. The list of articles in the category is no longer there.

But on the dashboard, the categories are still there and articles are linked to them. Does anyone have the slightest idea what could be causing this?