Make sure Trainz+ is pointing to the correct data folder.
Since you did a fresh install, the program automatically generates a new data folder. You can use the Launcher ----> Trainz Settings -----> Install tab to select your old data folder.
This will ensure that you have all your content.
If you have no other data folder, then you need to install all the packages you are entitled to as well as install content from the DLS. For your route that's missing track, right click on that in Content Manager and choose Download from the menu. This will download any dependencies you installed from the DLS. For anything else you obtained elsewhere. you will need to install those dependencies from the CDP files and Zip files that contain the assets.