BUG #16036: Segmentation fault while doing an update

The following bug has been logged on the website:

Bug reference:      16036
Logged by:          Антон Власов
Email address:      druidvav@gmail.com
PostgreSQL version: 12.0
Operating system:   PostgreSQL 12.0 (Debian 12.0-1.pgdg90+1) on x86_64
Description:

I am having segmentation fault like this:

2019-10-04 02:30:02 MSK [16919-6] LOG:  server process (PID 18415) was
terminated by signal 11: Segmentation fault
2019-10-04 02:30:02 MSK [16919-7] DETAIL:  Failed process was running:
update tracking.test_session set list_position = list_position + 1 where id
= $1
2019-10-04 02:30:02 MSK [16919-8] LOG:  terminating any other active server
processes

When there are several queries running simultaneously. Tried to get some
info from coredump, but that's all i have:

(gdb) bt
#0  GetMemoryChunkContext (pointer=0x0) at
./build/../src/include/utils/memutils.h:127
#1  pfree (pointer=0x0) at ./build/../src/backend/utils/mmgr/mcxt.c:1033
Backtrace stopped: Cannot access memory at address 0x7ffc990e7218