Object became invisible

I have a tunnel. When I put any object inside it and move away from the player, it became invisible…
Can’t understand, what’s wrong

Do you use occlusion culling? Open ‘Window > Occlusion Culling’ and try clearing it. If your problem disappears, you will need to play with the values in the ‘Bake’ tab, and bake it again (if you want to use occlusion culling).