untracked child process (PID XXXXX) exited with exit code 120

Hi,

I am running PostgreSQL 18.3 (Debian 18.3-1.pgdg13+1) (docker image)
and found this in my database logs the other day:

2026-05-07 18:39:13.947 CEST [1] LOG: untracked child process (PID 33254) exited with exit code 120
2026-05-07 18:39:13.947 CEST [1] LOG: terminating any other active server processes
2026-05-07 18:39:14.077 CEST [1] LOG: all server processes terminated; reinitializing

Anyone an idea about that untracked child process and what exit code
120 of that process would mean / want to tell me?

Thanks.

Torsten

PS: I used https://www.postgresql.org/search/ , but was unsuccessful so
far to get any hints on this, but maybe I just did not find the correct
question yet ;).