Problem Pairing Dell XPS 13 7390 Intel bluetooth btusb with some Headset / Speakers

Problem Pairing Dell XPS 13 7390 Intel bluetooth btusb with some Headset / Speakers

[Martin]

Dear all,

I do have a Dell XPS 13 7390 laptop running Ubuntu 20.04:
Linux martin-XPS-13-7390 5.11.0-38-generic #42~20.04.1-Ubuntu SMP Tue 
Sep 28 20:41:07 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
with Intel bluetooth card. dmesg recognizes it as:
usb 1-7: New USB device found, idVendor=8087, idProduct=0029, bcdDevice= 
0.01
It uses the btusb driver.
The driver / chip has problems to connect / pair with some headsets / 
speakers. Namely the Sony SRS-XB12 Mini speaker and the Teufel True Airy 
Wireless headset.
Pairing other speaker devices with the XPS works fine and the Sony and 
Teufel itself pair fine with other linux laptops / android smartphones. 
I'd like to concentrate on the Teufel, as I have logged the pairing 
conversation.
It looks like this on btmon:

@ MGMT Command: Pair Device (0x0019) plen 8            {0x0001} [hci0] 
8.822002
         BR/EDR Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Capability: KeyboardDisplay (0x04)
< HCI Command: Create Connection (0x01|0x0005) plen 13      #22 [hci0] 
8.822041
         Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Packet type: 0xcc18
           DM1 may be used
           DH1 may be used
           DM3 may be used
           DH3 may be used
           DM5 may be used
           DH5 may be used
         Page scan repetition mode: R2 (0x02)
         Page scan mode: Mandatory (0x00)
         Clock offset: 0x0000
         Role switch: Allow slave (0x01)
 > HCI Event: Command Status (0x0f) plen 4                   #23 [hci0] 
8.822352
       Create Connection (0x01|0x0005) ncmd 1
         Status: Success (0x00)
 > HCI Event: Connect Complete (0x03) plen 11               #28 [hci0] 
39.891457
         Status: LMP Response Timeout / LL Response Timeout (0x22)
         Handle: 65535
         Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Link type: ACL (0x01)
         Encryption: Disabled (0x00)
@ MGMT Event: Connect Failed (0x000d) plen 8          {0x0002} [hci0] 
39.891549
         BR/EDR Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Status: Timeout (0x08)
@ MGMT Event: Connect Failed (0x000d) plen 8          {0x0001} [hci0] 
39.891549
         BR/EDR Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Status: Timeout (0x08)
@ MGMT Event: Command Complete (0x0001) plen 10       {0x0001} [hci0] 
39.891575
       Pair Device (0x0019) plen 7
         Status: Timeout (0x08)
         BR/EDR Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)

So it pretty much looks like the laptop sends a connection request, but 
never sees a reply from the Teufel headset.

Same conversation for a Surface Pro 3 laptop (with some broadcom 
bluetooth chip if I remember correctly, also using btusb driver):

@ MGMT Command: Pair Device (0x0019) plen 8            {0x0001} [hci0] 
4.925811
         BR/EDR Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Capability: DisplayYesNo (0x01)
< HCI Command: Create Connection (0x01|0x0005) plen 13      #50 [hci0] 
4.925831
         Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Packet type: 0xcc18
           DM1 may be used
           DH1 may be used
           DM3 may be used
           DH3 may be used
           DM5 may be used
           DH5 may be used
         Page scan repetition mode: R2 (0x02)
         Page scan mode: Mandatory (0x00)
         Clock offset: 0x0000
         Role switch: Allow slave (0x01)
 > HCI Event: Command Status (0x0f) plen 4                   #51 [hci0] 
4.928927
       Create Connection (0x01|0x0005) ncmd 1
         Status: Success (0x00)
 > HCI Event: Connect Complete (0x03) plen 11                #54 [hci0] 
5.077961
         Status: Success (0x00)
         Handle: 1
         Address: 00:00:B0:05:65:67 (RND-RAD NETWORK DEVICES)
         Link type: ACL (0x01)
         Encryption: Disabled (0x00)
< HCI Command: Read Remote Supporte.. (0x01|0x001b) plen 2  #55 [hci0] 
5.078179
         Handle: 1
 > HCI Event: Command Status (0x0f) plen 4                   #56 [hci0] 
5.078928
       Read Remote Supported Features (0x01|0x001b) ncmd 1
         Status: Success (0x00)
[...]

What could cause the Intel 8087 / 0029 bluetooth chip / driver not being 
able to connect to the Teufel speakers?

There is also another report with a similar problem here: 
https://askubuntu.com/questions/1020584/apple-keyboard-a1016-pairing-fails
How to further debug this problem?
Is it necessary to buy some bt sniffer hardware to get to the bottom of 
this? I would invest in a cheapo 10€ sniffer like this 
https://www.amazon.com/-/en/dp/B081WRGL31 but I am not sure if they are 
sufficient to capture the pairing process.

kind regards
Martin