Cannot select some products combination

[onsy]

I have a weird problem and I cant find a solution.

Here is my page: https://www.vcb.si/domov/31-167-westin-shadteez.html#/35-barva-fire_perch/86-dolzina_cm_-7_cm

When i try to click on 3rd combination it doesn't select it. It redirects me back to first selection.

Can anyone help? Or maybe point me to JavaScript that handles stock and combinations, since products without stock are hidden.