While the game can be played offline, such as in airplane mode, for a short period of time, it is not meant to be played offline nor is it optimized for offline play for a long duration. As a result, when a player connects online again after playing offline for an extended time period, not all the data may be uploaded and synced correctly with our servers. Therefore, only some of the data will be uploaded a saved. It's our suggestion that all players connect to the internet while playing the game.
As of November 2020, the game no longer supports offline play.