B-17 Bomber Background Missing

I unlocked a background after completing an achievement with the B-17 Bomber. 

I believe it was 10 kills in a round and a Multi-kill. 

Post game, I immediately set it as my background. 

Yet, never saw it again. Now I can’t even find it in my Unlocked Backgrounds. 

Is there anyway to find this? I’ve actually completed the achievement a couple times again.
But .. no dice.