Diana Moonfall disabled

I was playing Diana a few days ago when my Moonfall skill became disabled after using it. I haven't been able to recreate it and I don't know much about the situation in which this happened as I didn't notice the problem until a bit later when I tried to use it. The ability was grayed in the HUD, as if it hadn't even been skilled yet, though I'd already used it previously in that game. However, I was able to use the skill again after I leveled it up one more time to level 2 and I didn't have any more trouble with the skill after that. I was in a Team Builder game with flash and smite and the base skin.