pc crashes while encoding

[Yash]

I am encoding a lot of videos at different bitrates and resolutions, I am also calculating VMAF score for each encoded videos. While doing this my pc randomly crashes/restarts regardless of the specific time, input video and the task (video encoding, VMAF calculation). I am using the following two commands:
Video encoding:

ffmpeg -hide_banner -loglevel verbose -nostats -i input.mp4 -crf 20 -maxrate 0.1M -bufsize 0.2M -s 640x360 -y output.mp4

VMAF calculation"

ffmpeg -hide_banner -loglevel verbose -i output.mp4 -i input.mp4 -lavfi "[0]scale=640:360[scaled];[scaled][1]libvmaf" -f null-

When i see output log after pc restart i only see following thing:

system configuration:
Description: Ubuntu 18.04.3 LTS
Release: 18.04
Codename: bionic
kernel version: 4.15.0-91-generic
gcc: gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
g++: g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
FFmpeg: 4.2.2
VMAF: 1.5.1

[Yash]

log_file

[Carl Eugen Hoyos]

If your computer restarts there is no bug that can be fixed in FFmpeg because crashes in user space programs like ffmpeg must never restart the whole system.
If you believe there is a bug in FFmpeg please test current FFmpeg git head, the only version supported here, paste the command line you tested together with the complete, uncut console output here in the ticket, do not provide screen shots. For crashes, backtrace, disassembly and register dump are also required, see: ​http://ffmpeg.org/bugreports.html

Your description almost certainly indicates a hardware problem.

[Carl Eugen Hoyos]

And please remove -hide_banner from your command line if you report an issue.