JIG works quite fine with custom lightboxes, usually a single line is all that's needed, like in the case of iLightBox in the Avada theme.
- Choose Custom Lightbox in JIG Settings > Lightboxes tab > Lightbox type (also for mobile) (screenshot).
- Add this to the Custom lightbox JS call setting:1$(JIG_selector).iLightBox(window.avadaLightBox.prepare_options("iLightbox[JIG]",false));