It is possible for the Android operating system to not fully disconnect from a Go Wireless system, leaving the sensor connected (thus showing the flashing green LED) even though the Go Wireless App is no longer able to receive data from the sensor. This is most common in the Android OS version 4.3.
The easiest way to get out of this state is to press and hold the power button on your Go Wireless sensor until the LED goes out. This will turn the sensor off. Pressing the power button again will power the sensor back on so you can continue to use the sensor normally.
Another way to resolve this issue is to restart Bluetooth on the unit that was last connected to this sensor. The challenge with this method is that it may be difficult to identify which device was the last one to connect to the sensor in a room full of students.