Having FooBox installed is just half of the story. Make sure you've selected it in JIG settings > Lightboxes tab as the active lightbox for desktop and mobile devices.
Have you forgot to tick FooBox settings > Justified Image Grid: Add full support for Justified Image Grid galleries. No other custom settings needed! option? No other FooBox settings are necessary to be ticked to make it work with JIG.
- If a different lightbox opens, check out this fix: The JIG settings I change don’t apply to galleries.
- Otherwise, if the desktop lightbox seems stuck for mobile devices: Mobile specific settings have no effect.
- JIG support doesn't cover setting up FooBox itself. Please contact FooPlugins support for more information.