So im vurrenty building a metro map, You start in the tunnel and you reach a station however there is a problem. When i tested it I came to the station and for some reason i could not see the main platform, But when i go up on it i can see it but not the railway wich i arrived in. The tunnel and the stations roof are made of concrete walls formed in a arch wich i copied and pasted over and over again if that help. The railway is also slight lower down than the main platform if that also helps.
Most likely it is the Occlusion Mesh causing that. Make sure in editor settings you check the box "Show Occlusion Mesh" It will show as a grayed out area underneath most objects. Some objects are not meant to be stacked. For instance if you place a sandbag on the roof of a dolpo house, the occlusion mesh of the sandbag goes into the house and when the player walks through the occlusion everything disappears until you get out of the occlusion. You will get it almost every time you stack buildings. Hope this explains it. Without seeing what you have it is hard to say. Stacking certain objects can cause a Nav Mesh Warning and show as a red cube when "Display Navigation Mesh " is selected.