Cannot connect to a BLE peripheral in nRF Connect Android app

[diode]

The peripheral is actually a dual-mode device, with BLE being a peripheral device.

I can connect to this device and discover the GATT services with the nRF Connect iPhone app and Master Control Panel 3.10.0 Windows application without problems. However, I cannot do it with the nRF Connect Android app (which doesn't even pass through the connection stage). The debug log is:

nRF Connect, 2016-07-29
ABCDevice (xx:xx:xx:xx:xx:xx)
V	12:44:41.583	Connecting to xx:xx:xx:xx:xx:xx...
D	12:44:41.593	gatt = device.connectGatt(autoConnect = false)
D	12:44:46.918	[Broadcast] Action received: android.bluetooth.device.action.ACL_CONNECTED
D	12:44:46.944	[Callback] Connection state changed with status: 133 and new state: DISCONNECTED (0)
E	12:44:46.960	Error 133 (0x85): GATT ERROR
I	12:44:46.969	Disconnected
D	12:44:47.031	[Broadcast] Action received: android.bluetooth.device.action.ACL_DISCONNECTED

This log doesn't seem too informative. It doesn't work on Android version 5.0 and 6.0. Does anyone know what this problem can be?

[Hung Bui]

@diode: Which Android device did you use ? Have you tried to remove bond information (Forget this device) in Bluetooth setting and try to turn off and on Bluetooth ?

[diode]

@hunghui I tested it on Samsung Galaxy Note 4 and Nexus 6P. Both show this behavior. I was trying to get air trace with nRF Sniffer, but this device doesn't even show up in the advertizer list (although I can see it on nRF Connect app). Some other people report something similar (see this post). I am feeling this has something to do with the dual-mode device talking with an Android device.

[diode]

I may have found the cause of the problem. The dual-mode BLE flag data of the peripheral was 0x020102, which didn't indicate the dual-mode property. After setting it to 0x02011A, nRF Connect Android app can connect to the peripheral.

[Hung Bui]

@diode: I'm not familiar with that "dual-mode BLE flag" what is that ? Is it a flag in the advertising packet ?

[diode]

Yes, this is the flag data in BLE advertising packet payload.