Created attachment 289003 [details] Packet dump of the failed connection attempt on Linux I have a problem connecting Sennheiser Momentum True Wireless 2 headset over Bluetooth. The headset says "Connected" and then reboots immediately after. After reboot the headset says "Power on" and tries connecting again, and fails the same way, and so on. From the Bluetooth packet dump it looks like the problem happens after bluetoothd sends AVRCP ListPlayerApplicationSettingAttributes message to the headset. The headset sends Not Implemented response and then reboots. In the response Wireshark shows warnings about encoding issues. I'm attaching a packet dump captured from one of the connection attempts. The ListPlayerApplicationSettingAttributes message is in packet 262 and the response is in packet 264. This is on Kubuntu 20.04. I tried bluez 5.53 from Kubuntu and revision 3146b7a0785758be2d4e894d44e99d29c0db983e from git master - the behavior is the same. I've also verified that the headset does work on Windows 10. On that system, ListPlayerApplicationSettingAttributes is not present in the packet exchange. Also, the headset does connect if AVRCP is disabled by adding --noplugin=avrcp to bluetoothd command line.
Created attachment 289005 [details] Another failed connection attempt on Linux, in btsnoop format
Created attachment 289007 [details] Packet dump of a successful connect on Windows. Use Decode As -> Bluetooth in Wireshark.
For the record, the problem happens with headset firmware versions 4.5.0 and 4.6.0 (which is currently the latest one).
Should be fixed by bluez commits b7fe84c4582a54e098c0f52500d0ed7396026d05 and ba91d0ad7379fc7b064af911229e50ffa1a16169.