For nearly a year we have not be able to upgrade our 1000+ Android devices operating with 4.1 Jellybean because the Bluetooth will not work properly. We recently discovered that this problem apparently began with Android version 4.2, coinciding with the change in the Bluetooth stack from BlueZ to Bluezoid. Here is the story: We use an Anoto digital pen with bluetooth and an app we developed, installed on an Android device (Kyocera Torque cell phone). After pairing the pen with the phone, individual transactions, written by the pen on paper are sent to the phone after a "send" box is checked. The phone then responds by activating its camera, pictures are taken then pen data and photos are sent to our server. This is the process which has been working flawlessly. The problem: After 4.1, the pen must be paired then the phone restarted. The "send" box must be checked twice before phone responds. After 8 sends, the process reverts to the correct process and remains until 20 total "sends" upon which the bluetooth function stops. The phone must be restarted. The pattern repeats. We have tested this on a variety of devices using Android 4.2 all the way to Marshmallow, all with the same results.
Please respond if you have some ideas which might help. We're hoping to find some work-around which does not require a major code re-write etc.