In foundation 6 there is a bug that leaves the reveal background overlay open if you return using the browser navigation.
Follow this scenario:
1: trigger modal
2: let's assume withing the modal we have a button that takes us somewhere else. We click on that btn.
3: Once we are on a new page we click back, using the browser back btn
4: Result ---> THE OVERLAY IS STILL THERE.
And all the body classes etc are still applying, but no modal or actions to close it.
I had to manually close the modal every time I load the page to fix this....