I've had several Career scenarios that have disappeared, always after I have marked them as Favourites and saved their sessions (intending to resume them later). The scenarios still exist, as I can see them if I go into Build rather than Drive, but I can't resume a session in Build. I've learned not to use Favourites anymore, but does anyone know of a way to get the lost sessions to reappear?
I hope Trent Valley, Preston to Crewe, Tadami and Thames Branches all release in June, then with the Steam Summer Sale four weeks away, it will be a very exciting month.
The primary reason to lose scenarios is uninstalling the route. Scenarios in otherwise empty folders do not normally show up in the menus, but they do when filtering. (You can press Start and cause an instant crash.) Also, some scenarios do or do not show up when filtering (only the other), I recall some Koblenz-Trier ones. You can also delete your cache to force a full rebuild, in case something got funny. The last reason I can think about, albeit very rare, is corrupt workshop scenarios showing up in the wrong place, then upon fixing them they move. Although in this case it usually ends up under free roam, just like season is spring and weather is standard (2d cloudy).