Seems like after the upgrade, a number of people have had the problem with randomly missing categories from the admin panel/dashboard. One of mine randomly disappeared after I renamed it. It was no longer a subcategory and was at the bottom of the list (not alphabetical order) on all the filters etc., but refused to show up in the Categories admin panel.
So, I found lots of information on how to fix missing categories for wordpress, but not when you use wordpress.com. After much searching, I found one solution on wordpress.com forums (second last reply), but what’s missing is the key element on how to figure out your category ID. Easiest way then:
Find your category ID by looking at the source code for your blog. You will see for example, <li class=”cat-item cat-item-78954″>. The number is your category ID. Similar thing for tags.
You must have categories (or tags) displayed on your blog for this to work obviously.
Learning (Lib)Tech 