Hello,
Your issue is related to some CSS of your template and the fact that you have a "div" which is hover the image listing (on mobile screen).
So when you "touch/click" on the images ; you click on the div and not on the image ; so the popup cannot load since it do not receive the event.
By cleaning the CSS of the template and fixing that overlap, the popup is working fine.
Please note that kind of help is outside the limit of our support.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.