colorbox-load pop-up is not working

Whenever a user taps on an image on my webpage, that specific image should pop-up(enlarged) on a same window and when I close that image it should stay on the same window as I was before, and that is possible with the colorbox-load. But why is it not working for me.

Interestingly, the same code, placed at different places on a same page on a different content, is sometimes popping out the image and sometimes it just opens the new window on the same window which is weird.

Why is this peculiar behaviour? Please let me know where I am going wrong? I want it should always pop-up.