Instanciated class in contextMenu destroyed on play

Hi ! I'm a student in game dev and as i'm starting to feel confident enought to test new things i tried to make an A* pathfinding.
But the probleme is that to prevent lost of perfomance with a lot of nodes i made a methode that i can run in context menu to Pre-fill my grid of nodes and that Grid and all the instanciated nodes are destroyed as soon as i click on the play button.
is there something i'm doing bad ?

here are my node class and pathfinder class