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.
Also try:
- 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.