Categories Not Working After Update

I had posts assigned to certain categories to control what’s posted on the homepage and other pages. It’s been working fine until I updated wordpress this morning and now all the posts are not in any categories. Not even uncategorized, and when I try to assign posts to a category, nothing happens at all. I check the box next to the category and click update, and the page reloads saying “Page updated” but the category box remains unchecked. I tried changing the permalinks and deleting the cache. I also tried adding new categories, they add fine but the posts still won’t attach to the category.

Please help!