Accept() error in secure sockets.

[Nulllix]

Introduction

Hey, everybody!
I have an nRF52840-DK debug board on which I am trying to run BSD Secure Sockets on up the IPSP.
I used the echo server (advanced) example as a basis.
My code on which the problem is stably reproduced is here.

Problem

I have written a small python script that I'm trying to use to connect to my server. When I try to connect to nRF52840 with it, HardFault occurs in accept(...) function:

I have enabled additional logs inside the bluetooth stack and as you can see, at some point the pointer to user_data takes an invalid value.

Callstack which leads to HardFault:

Using a debugger I was able to get the full callstask which causes this error (inside bt_conn_send_cb(...) the functions you see in the screenshot above are called):

BIG SCREENSHOTS WITH CALLSTACK

The full log with the error and callstack in text form, can be found here.

How to reproduce?

1. Clone my repository.
2. Build and load firmware to nRF52840 from it.
3. Connect BLE adapter to PC (i use TL-LINK UB400)
4. Use script board_connect.sh to activate the 6lowpan and connect it to the board.
5. Use python script test_conn.py to connect to the sockets.

Has anyone ever encountered anything like this?