I leveled my hunter up to 2 and received two cards of "animal companion", but my game crashed after that and when I re-logged the cards were gone...
I'm having the same problem!!! I kept leveling and the same problem happened for my lvl 4 rewards as well! I'm a lvl 5 Hunter and only have 10/20 basic cards :(
I have the same issue with some basic priest cards I got from levelling up. I want to put them in my deck too :'(
I had this issue too. I got to level 8 with my druid and received the swipe reward. I added it to my deck and attempted to play a practice game. Hearthstone crashed before the game started, giving me the pixie error screen. I logged in again and the druid deck was unplayable with a big red X over it, and it turned out the Swipe cards were missing.