Done the obligatory refresh, my site was also upgraded to SSL today.
Just setting up the Shop so only had 1 item which until today showed correctly with a pop-up window not each image when clicked opens in a new separate window.
not an OC-related problem, but something with your Custom Theme.
For Sale: Turnkey URLs with Opencart installed
Present Opencart LIGHT Testsite: http://www.velomech.ch
Attacker IP Blocks are denied from further access to my Sites!
Just contact me for more Information at: email@example.com
730+ FREE OC Extension-Repositories - from OC v.1.5.x up
on the largest Opencart-Mod Github Site: https://github.com/IP-CAM