Hi there,
Thank you for the information. I did test the case on my local installation and it is working ok with no problem. I set the Post Type to be Media Library and I assigned a Category Filter and it shows with no problem.
The same thing is not showing in your installation. I added a Test Page on your installation and it does not show the images.
The difference is that I used The Grid version 2.6.0, but you are using the version 2.5.5.
Please make a complete backup of your website and delete The Grid plugin from your installation. Then Go to X > Validation and install it again from the Extensions section of that page and enable the plugin.
If you still have the problem please deactivate all plugins except Cornerstone and The Grid and test the case.
Also please deactivate the CloudFlare and change it to the devloper mode for your testing.
Thank you.