I've returned to K2 using a commercial template - the behaviour of the item images opening in light box preview is not predictable.
The image opens in a separate window and site visitor needs to click browser return. to K2 item page.
Is there an option to disable the preview image or a place to investigate the falure of lightbox.
I've read a post from 2012 about commenting out a line of php. However K2 has developed and that line does not appear in the file.

SOLVED in next message

Hi

It SOLVED

Need ON load jQuery in K2 preset!
imgur.com/JGwP3J1

Clear cache and after it all work OK!

WBR,

Igor

Since this issue can be related to other extensions or a misconfiguration, check the console tab of your developer tools for any potential errors.

I found the solution, the template was very clean with no jQuery library loaded, I enabled the load v1.12.4 in K2 Parameters and lightbox immediately started to function on item images.

Thank you for letting us know Ian :)