If you went to your seller page only to find that all of the categories on the left that your items are grouped into is gone, don't worry. Before, when you clicked on your username, it would take you straight to the page that had all of your items listed in groups...
.
Now...when you click on your username.. you get this...

To see your category listings simply scroll all the way down and click on 'SEE ALL' and it will take you back to the original seller page. I for one use the category links often when listing items. It helps when posting similar items instead of scrolling the listings on the overview page in the seller hub. Hope this helps because I was completely lost and upset when I couldn't find the categories.