Disappearing skins I got from friends

When Snow Day Bard was out my freind sent it as a gift to me... Then it just suddenly disappeared. I didn't care back then because I've stopped playing Bard a lot. But a couple weeks ago when Death Blossom Kha'zix was out my freind gifted it to me. But a 2 days ago I was in draft pick and I clicked on kha. But the skin was gone. Anyone know why? Twice now my skins gifted by my friends have disappeared. If you can offer any explanation, please do.