You just upgraded WordPress and “My Category Order” (widget and functions) do not display any categories.
I hate to be you! But wait…
This is normal and you can fix it very easily by visiting the “My Category Order” page. When you visit the plugin page the first time after a WordPress upgrade, it will show this message:
File /home/advokata/public_html/wp-includes/taxonomy.php has been patched successfully
This is the solution Andrew (plugin author) pointed out by email after I commented on the “My Category Order” plugin page.