After upgrade, the admin editor for a post has all categories unchecked. The categories are saved and accurately displaying on the front-end as both the sidebar category list (with counts) and as the breadcrumbs/tags on each post, but editing and saving an article removes all categories unless they are re-checked on every round of edits. If all categories are rechecked, upon saving, the editor refreshes and the categories are all unchecked again.
Any insight? I looked through my plugins and don't see any that are related to categories. I deactivated any that weren't essential.