Have you checked to verify the web server has full permissions throughout the var directory? If that's not the problem, you'll want to check debug output.
The VAR folder and it's subfolders are all set to 777 to remove any permissions issues.
I can see similar to the following in the debug output:-
The reference alias original file var/plain_site/storage/images/galleries/volutidae/amoria-maculata-caroli/2804-1-eng-GB/Amoria-maculata-caroli.jpg does not exist
But this file does exist at the location specified. Should it have public_html at teh beginning of the URL?