Unfortunately, from time to time, unexpected errors can occur within the app causing it to close during a workout session.
Loosing workout data is never fun which is why the app tries to recover your lost data when it re-opens.
In this case, if you receive a notification that the app detected an unsaved session, simply choose to save it and the recovery process is complete.
On the other hand, if the app doesn't detect an incomplete session, you might still be able to recover it by tapping on the WORKOUTS tab in the iPhone app and then on the IMPORT at the top left. The app will look through your HEALTH app workouts. If you find your session it can then be imported.
If the app closes unexpectedly on multiple occasions, there might be an underlying issue that we need to address. Please enable the DEBUG LOGS from the MORE tab in the iPhone app and send them to us for further analysis.