This means that the device has failed to read the TAG. The app may have lost contact to the TAG during reading and the loading of data is interrupted.
When reading, keep the phone steady and wait for a vibration feedback. You may have removed your device too quickly for it to read properly or to finish reading.
If the problem continues, try closing the app and open it again.
How to read out temperature TAG using Android: https://vimeo.com/377511387
How to read out temperature TAG using iPhone: https://vimeo.com/357559756
If this doesn't work, please contact TAG Sensors.