This happened to me, too, after the upgrade. Most of my posts are visible except one category, but when I’m in the dashboard and click on “posts”, it says I don’t have any. Though I know the posts still exist in the database because the correct number of posts is listed next to the “post” link. It seems to me there must be a disconnect between the dashboard and the database, but I can’t figure it out. My $table_prefix is the default ‘wp_’ and so are my WP tables.