Check the device's battery level in the App. Replace a new CR123A battery if it is too low.
If you recently relocated your device, try to move the sensor closer to the hub.
If you recently relocated your smart hub. Try to move it back to its original places.
Update your smart hub to the latest firmware and update your App, then setup up the sensor again.
If the above steps cannot solve the problem, feel free to contact us via firstname.lastname@example.org.