Blueprint works but i get an error after playing game


So what i’m trying to do is get the pawn speed as a variable and then use it to set my blendspace so when the pawn gains speed the things on the side opens up. I can do it without a problem.
But when i close the game i get this annoying error. it doesn’t ruin anything but i wanna create clean project so it annoys me and i want to know why.