No thumbnails on WPMU setup

I’ve been using this wonderful plugin on separate sites with no issues at all. But now I’m pulling several sites into a WPMU network and it doesn’t work.

It picks up the post titles and everything else but it just won’t generate the thumbnails. I presume this is something to do with the cache and the way WPMU uses a single version of the plugin and messes around with subdirs and stuff.

Is there a way to fix it?

https://www.ads-software.com/extend/plugins/category-grid-view-gallery/