As of the latest PBE patch (12/13), Neon Vi and Masked Shaco are not available for purchase and you cannot use them in game, even if you bought them in the past. That is something we did on purpose so you shouldn't report it as a bug.
Some of you might notice that Exiled Morgana has been removed from your accounts by mistake. The skin is still available for purchase in the shop, so you can go ahead and re-buy her.
Sorry for any inconvenience!
Update: Masked Shaco is back on PBE.