After importing an asset pack my camera falls through the ground or in the sky.

I purchased this asset pack. Unity Asset Store - The Best Assets for Game Making I flattened an area of terrain and placed these down. I dragged my camera with my gun and it’s bullet spawn over to the new area to test it out. I saved. I pressed play, and my camera, gun, and spawn fell through the ground. I added a rigidbody and it makes it fly in the sky. Here is a screenshot. 20845-glitch.jpg

please don’t suggest making sure my terrain has a collider or my camera is above the ground. Those are fine. What should I do?

ps. also I fall through anywhere on my entire map. I can’t put a picture here because I’ve exceeded the max size for this post. I’ll post a comment.

Thanks, but I decided to just make a new scene. That one was sort of a basic sketch of the actual scene for my game, but I am working on the full level now. I will consort to these answers should the problem arise again, as well as anyone on the internet who has a similar problem and is looking for answers. Thank you.