Hi Ramanand,
All SensorTags (including all sensors) are tested in production so they should be functional. I've experienced the same issue a few times, and when I had these problems the issues were related to Apple's core Bluetooth implementation.
Try to turn on and off Bluetooth on your iOS device and see if that resolves the problem. You might also need to shut down the app by double clicking on the home button and the close the app.
Best regards,
Espen
