This happens because the Wave and the app synced but it hasn't yet sent the updated data to the cloud.
The Last Sync in the app is referring to the synchronization between the Wave and the app. This happened whenever you phone/table is within the Bluetooth range, the readings will get to sent to your app from the Wave. The app will then send the updated data to the cloud when connected to the internet.
To check the Last Cloud Sync:
- tap on the hamburger menu on the top-left corner of your screen
- tap on Devices
- tap on My Devices settings
- select your current device
- Tap on Sync Info
- See Last Cloud Synced