Hi,
I had a similar problem one month ago trying to connect a joystick in bluetooth to a RPI3 running stellarmate.
Following an advice given by Jasem, I updated BlueZ:
sudo add-apt-repository ppa:mutlaqja/bluez
sudo apt-get -y dist-upgrade.
Since this, BT works reliably.
Maybe it could help :)
Pierre-Yves

Read More...