Unity not working right after build and run

Hello! after i hit build and run one fine day I was surprised to see that a platform in one of my levels was missing. Intrigued I looked into the editor as this platform was clearly visible there. I hit the play button and it dissapeared. My enemies also wouldnt walk towards the player, they walked in a straight line then stopped. I had made it so that when you collect a key, a wall dissapears. On certain levels this never happened and on some of the later levels the keys werent even rendered. What happened? And how can i fix this. It all worked fine before this.