Aram Skin Boost not giving skin forever [Gameplay?]

While in the lobby for an ARAM match ( just after patch 5.14 ), a teammate of mine purchased a skin boost. We all got to use those skins in the game, and we all got the 100 IP boost. However once the match was over, the skin had gone away. It was "Battleborn Kayle." Oddly enough, a few days before this ( and also prior to patch 5.14 ) I got "Riot Kayle" the same way. I did not lose that skin. Could there be a bug that caused me to lose the second Kayle skin I had gotten through the ARAM skin boost?