For missing assets try one of the following remedies.

1. ensure your install path is correct, if you have a non-default install path check to make sure that the addons are not installed in the default path or somewhere else on your computer.

the default install location for Run8 V3 is

C:\Run8Studios\Run8 Train Simulator V3

2. Check to ensure your antivirus or windows defender is not blocking the installation of addons.

If you have missing track and signals on a loaded route.

If you want all the routes in the region to load, you can leave the routes unselected (or multi-select all of them). If you only want certain route(s) to load, multi-select them as desired.

If you don't see track or signals, but do see other terrain and scenery, you most likely either didn't select that particular route, OR, you don't yet own that route but parts of the scenery were updated in a regional update.