Thumbnails not showing up

Hello,

I love the plugin and its working great.
Except its not showing my thumbnails on the main blog.
I enabled the function on the settings.

I use Modernize as theme, anyone having experience with this?
Modernize has a page builder with custom functions for showing the blog items.

If somebody could help me that would be great.

Thanks

https://www.ads-software.com/extend/plugins/wordpress-mu-sitewide-tags/