Just purchased the Class 20 dlc for Xbox X and it does not appear in game. Game manager says it is installed.
To ensure everyone is on the same page, can you confirm that you have Tees Valley Line installed? The Class 20 will not work without it.
Just as a warning, if purchasing a loco dlc for a pre-TSW3 route, you will also need the route it runs on.
Yeah it is difficult keeping track of which ones do that and which ones don't. If you are not sure, you can ask the forums.