MTU Exchange - Not receiving a rsp

Hi Nordic,

I am working on a NRF52 DK with the example code ble_app_interactive. I am using the NRF52 DK as a central and trying to connect to a peripheral hearing aid. My problem is that when I try to connect to the hearing aid, I get Connected and then immediately Disconnected with the error code 0x3E, as seen on the log:

=~=~=~=~=~=~=~=~=~=~=~= PuTTY log 2018.12.07 13:23:09 =~=~=~=~=~=~=~=~=~=~=~=

uart_cli:~$ BLE app with command line interface example started.
uart_cli:~$ Press Tab to view all available commands.
uart_cli:~$ scan onScan started
uart_cli:~$ <info> app: Scanning
uart_cli:~$ devicesDevice 00:16:94:1A:73:36 PXC 550
Device 5C:29:EE:53:12:63 ac_hi_test_hi_ECC5
Device C8:0A:9C:09:3E:38 Tile
Device 5A:4D:70:0D:7C:84 arhs
Device 62:9F:F4:7F:29:4E [LG] webOS TV UJ634V
uart_cli:~$ connect arhsuart_cli:~$ uart_cli:~$ <info> app: CENTRAL: Connecting...
uart_cli:~$ Connected to address: uart_cli:~$ 5A uart_cli:~$ 4D uart_cli:~$ 70 uart_cli:~$ 0D uart_cli:~$ 7C uart_cli:~$ 84 uart_cli:~$ 
uart_cli:~$ <info> app: CENTRAL: Connected, handle: 0.
uart_cli:~$ <info> app: CENTRAL: Disconnected, handle: 0, reason: 0x3E

I have an ellisys sniffer, and in the trace, I can see that the Connection Indication Packet is send, and then an ATT Exchange MTU Request Packet is send, but I think that the peripheral I'm requesting the MTU from, can't send MTU before it is paired. The trace is shown below:


I also have a sniffer on a connection from a mobile to the same peripheral, using the nrf connect app, and this works without problem, this is the trace:


If it is the problem with that the peripheral can't send MTU before it is paired, can I change that sequence in my progam, so that it doesn't make MTU exchange at that point or maybe this isn't the problem?

BR Dresse.