Site Categories not updating landing page?

The Site Categories landing page is not updated with new sub categories or blogs (sites) created on the network.
What could be the issue? I have a caching plugin (W3 Total Cache) installed but it is not activated.
I should add that there is now three blogs installed on the network and linked to categories, but only one is picked up by Site Categories. Similarly, two subcategories are displayed, but the third and last one created is not reflected on the landing page.
The site has WP Multisite, BP, bbPress and a host of other plugins installed.