https://www.gamespot.com/articles/fortnite-season-6s-big-new-item-shadow-stones-are-/1100-6462257/

One of the major new items Epic Games introduced to Fortnite at the start of Season 6 was Shadow Stones, but they've been beset by problems since arriving. Shortly after the stones went live, the developer had to pull them from the game several times, but it appears those issues have finally been resolved, and Shadow Stones are now back in the game.

The problems first began soon after Season 6 kicked off last week. Epic announced that it had to temporarily disable the Shadow Stones due to a bug. It didn't elaborate on what that issue was, but players had discovered an exploit that allowed them to shoot their weapons while being invisible, which wouldn't normally be possible when the stones were used.