Many players experience a issue with Steam Cloud sync, which manifests as

• Partial and one-way sync
  Progress syncs to new devices, but the updated progress does not back to old ones.
  
• False success
  Steam is always showing "Up to date", but saves are actually conflicting.

Local saves upload to the cloud normally, but updated cloud saves fail to download or overwrite existing local files.

This prevents devices with local saves from downloading updates, while new devices without local saves can still download cloud saves.

Manually transfer "save-file.bin" between two devices.

Delete the local save folder (or specifically "save-file.bin") to trigger automatic cloud sync. The directory is

• Windows
  
  %UserProfile%\AppData\LocalLow\Oroboro games\TrainValley2\
• macOS (Press Shift-Command-G to open a Go to Folder window)
  
  ~/Library/Application Support/com.Oroboro-games.TrainValley2/
• Linux
  
  ~/.config/unity3d/Oroboro games/TrainValley2/

Caution! Back up files or ensure the trash folder is available before deletion.

This ensures the saves are up-to-date on next launch, and not in conflict due to any manual modification.