at jobs don't clear the queue even when completed?

I have some very simple python code that sets up a job queue, piping to the linux batch command:

import subprocess

for j in range(1,17):
  process = subprocess.Popen('/bin/sh', '-c', f'python test.py {j} | batch')
  process.communicate()
  print(process.returncode)

When I run this, the print(process.returncode) line prints 0 which means success.

The script being called in the subprocess, test.py, just writes a quick txt file so nothing resource consuming:

import sys

with open(f'{sys.argv[1]}.txt', 'w') as f:
    f.write('hello')

This code creates 16 jobs and appears to run them all at once (batch is kinda pointless in what I'm doing at the moment since the server never reaches a load where it needs to queue jobs, but I'm just learning right now). Immediately after running it, when I type atq in the terminal, I can see that none of the jobs are running (no = or b), but they also don't clear the queue despite the seeming success given that they write the text files and give me a returncode of 0. What could be the reason for them to not clear the queue? If it's a hidden error, how would I go about getting that output?

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