GBGames: I just downloaded it, installed it (to ~/Games/TrainValley as opposed to the default location), and ran it on my Ubuntu 18.04 system. It plays fine, but after finishing the first stamp (Nederland), I closed the game to install the Germany DLC.

When I reopened the game, I saw the previously completed stamp looked pristine and the next level wasn't available like I expected. I even tried playing the next level on my next playthrough, and I could see it was completed as well, but when I shut down the game and start it again, it's no longer completed.

I tried three separate play sessions, and I find that the game isn't saving progress. Is there a bug preventing it from working correctly? I assume the game persists.

I do see some logs appearing that indicate that this game, despite being from GOG.com and not Steam, is expecting to find the Steam API.

$ ./start.sh
Running Train Valley
Set current directory to /[my_home_directory]/Games/TrainValley/game
Found path: /[my_home_directory]/Games/TrainValley/game/train-valley.x86_64
Mono path[0] = '/[my_home_directory]/Games/TrainValley/game/train-valley_Data/Managed'
Mono config path = '/[my_home_directory]/Games/TrainValley/game/train-valley_Data/Mono/etc'
Preloaded 'ScreenSelector.so'
Preloaded 'libCSteamworks.so'
Preloaded 'libsteam_api.so'
Unable to preload the following plugins:
ScreenSelector.so
libCSteamworks.so
libsteam_api.so
Display 0 'LG Ultra HD 27"': 3840x2160 (primary device).
Logging to /[my_home_directory]/.config/unity3d/Oroboro games/Train Valley/Player.log
[S_API FAIL] SteamAPI_Init() failed; SteamAPI_IsSteamRunning() failed.
[S_API FAIL] SteamAPI_Init() failed; unable to locate a running instance of Steam, or a local steamclient.so.