BPI M2+ Android 7.0: BLE work but doesn't complete the pairing


I installed on BPI M2+ Android 7 Nougat, as the operating system. I tried to use Bluetooth and this works correctly as I was also able to send photos from an Android phone. So far so good. I found a problem using two applications that allow connection to two devices via Bluetooth. In the first case, I used a Movesense application that has to connect to a wearable device that mounts a Bluetooth Low Energy. The devices are identified within the application and by clicking on the identification the pairing procedure begins. At this point we have a problem, in fact, the coupling does not materialize but it is as if it remained in an “infinite loop”. In the second case, I use an application that allows connecting via Bluetooth to a sphygmomanometer fitted with a Bluetooth 4.0 with low power consumption. Also, in this case, the device is identified but when the coupling must be completed the application crashes. Analyzing the two problems, it is as if the BPI M2 + microcontroller saw the Bluetooth devices inside the application but could not connect to them. What could be the problem since the Bluetooth outside the application works?