sounds like a bug to me, it shows you got it this year, my first skin out of the 50 i own was an ashe skin, and i still have it. if your first thought is to blame riot for cheating you out of money, that is sad.
everyone just stop purchasing the skins, cause the Riot company will cancelled your owned skins after a period of time, and they hope you won't remember purchasing them, then earning your money again and again. I posed this situation on tweet, and I swear to God I'm telling the truth.
https://twitter.com/Zach_CTR/with_replieshttps://twitter.com/Zach_CTR/with_replies
https://twitter.com/Zach_CTR/with_replies
I got more evidence
So I 'm purchasing the same skins, again and again and again and again !!!
Don't blame riot, its probably a bug. send a support ticket before claiming they intentionally take away your skins.