The missing ground textures on the route is usually caused by TS Academy not being installed.

To check you have TS Academy installed: 

1) Open Steam

2) Click Train Simulator on the left-hand side

3) Scroll down slightly until you see the DLC tab on the right. Click "Manage my DLC".

4) Type "Academy" in the box. 

5) Make sure the box next to "Academy" is ticked. If it's already ticked, untick and re-tick it then load up Train Simulator and see if the issue has been fixed.