Bluetooth on Android : cannot achieve any peering for Qt examples

I tried Bluetooth with theses examples: btchat, qml chat, pingpong, scanner
between a Linux computer, an Android 5.0 device and an Android 4.1 device.

• scanner take some times but reports services between Android devices
• pingpong can detect (sometimes) a server but stuck on configuration
• device detection take a while

Thus I cannot achieve any data exchange.

I can try to debug if someone has a debugging procedure.