The following program frequently raises a ProcessLookupError exception when calling proc.terminate():

```
import threading
import subprocess
import multiprocessing

proc = subprocess.Popen(["sh", "-c", "exit 0"])

q = multiprocessing.Queue()

def communicate_thread(proc):
    proc.communicate()

t = threading.Thread(target=communicate_thread, args=(proc,))
t.start()

proc.terminate()

t.join()
```

I'm reproducing this with Python 3.8.2 on Arch Linux by saving the script and rapidly executing it like this:

$ bash -e -c "while true; do python3 test.py; done

The (unused) multiprocessing.Queue seems to play a role here because the problem vanishes when removing that one line.