If one of your upgrades didn’t finish properly, you most likely had a connectivity error somewhere along the way.
Based on your device’s connection specifications, “Lost Connection Warnings” can take up to a few minutes before turning up in the game. As a result of the delay, you may continue playing as usual before being notified, however any progress made during this period will not be saved.
These errors will occur due to a variety of reasons, including but not limited to: poor Internet connection, server issues, ISP errors and/or device performance.
Any accidentally cancelled upgrades will refund half of the upgrade price back to you. If you suspect that this might’ve happened, you might want to ensure you lock your device after each playing session.
To avoid these issues in the future, I recommend checking our “My game crashes” article via the Help Center.