Supervisord stopped working on 80% of droplets at the same time

I have supervisord (latest version, 4.2.0) on my ubuntu 18.04 droplets in different regions.

Today I saw that exactly at the same time almost all of droplets has dropped in CPU usage from 20-30% to almost zero. It turned out that supervisord stopped working.

In supervisor logs I can see that someone send SIGTERM:

2020-05-16 12:33:59,831 WARN received SIGTERM indicating exit request

The only relevant answer I googled is https://stackoverflow.com/questions/28440543/supervisor-gets-a-sigterm-for-some-reason-quits-and-stops-all-its-processes

However, I’ve checked out that the date of unattended upgrade is different, though minutes are the same, which is suspicious:

Start-Date: 2020-05-15  06:33:13
Commandline: /usr/bin/unattended-upgrade
Upgrade: libjson-c3:amd64 (0.12.1-1.3, 0.12.1-1.3ubuntu0.1)
End-Date: 2020-05-15  06:33:13

Notice that both hours and days are different.

Is it possible to somehow figure out why supervisord stopped working, and how can I prevent this to happen in future? Since it’s crucial for me, I need it up and running for 100% of time :(