A bit hard to diagnose without seeing your custom X3 javascript code, which you now have removed in place of another popup. I took a look at Danjel's website, and I can see the problem. Either the plugin changed, or more likely, Instagram changed their API output, because their image url's now look something like this (
note the last part):
href="//scontent.cdninstagram.com/vp/7c467bebbc30324129b50871c3a26f05/5C982E1C/t51.2885-15/sh0.08/e35/p640x640/46352168_924230287773058_2633442970289318963_n.jpg?_nc_ht=scontent.cdninstagram.com"
With an URL like this, X3 popup can't know it's an image, because it doesn't end with an image extension. Thus, the only way to display non-image content, would be by using iframe. You need to tell X3 explicitly that the HREF is an image, by using
data-popup-image attribute (instead of just data-popup).
<a href="https://d.pr/i/3SjM+" data-popup-image>Force popup image-type</a>
Reference to this in
popup examples.