During a game while having Displacer Kitten on the board. I cast a noncreature spell during my opponent's turn which then would trigger DK. For some reason when I would exile the card targeted it would not return to the battlefield.. So I am confused as to why this occurred but wanted to bring this up since it makes DK not work as intended and causes my board to be affected and loose the advantage due to this.

Help? P.S. This happened while playing on PC.