In the Alert app you can find information related to the state of your Embrace data. Open Alert app>>More>>Settings>>Advanced Settings to view the info.
Last Sync to Cloud indicates the last time data was sent from the Alert app to Empatica cloud servers. Make sure your phone is connected to internet to keep data synced. If data is not sent to Empatica cloud servers, you will not be able to see your rest, sleep and activity information in the Mate app.