Strange behavior of Local executor

[borisovpavl73]

Hi!

Running airflow standalone ver 3.0.4 in WSL2 on Windows11.

With this example of code i want to watch how Airflow can control order of task execution.

import pendulum
from airflow import DAG
from airflow.providers.standard.operators.python import PythonOperator


def tst_func(name):
    print(f"hello from task {name}")

with DAG(
        'dag_tst_tasks',
        schedule='@daily',
        start_date=pendulum.now().add(days=-1),
) as dag:

    t1 = PythonOperator(
        task_id="t1",
        python_callable=tst_func,
        op_kwargs={"name": 1}
    )

    t2 = PythonOperator(
        task_id="t2",
        python_callable=tst_func,
        op_kwargs={"name": 2}
    )

    t3 = PythonOperator(
        task_id="t3",
        python_callable=tst_func,
        op_kwargs={"name": 3}
    )

    t4 = PythonOperator(
        task_id="t4",
        python_callable=tst_func,
        op_kwargs={"name": 4}
    )

    t5 = PythonOperator(
        task_id="t5",
        python_callable=tst_func,
        op_kwargs={"name": 5}
    )


    t6 = PythonOperator(
        task_id="t6",
        python_callable=tst_func,
        op_kwargs={"name": 6}
    )

    t3 >> [t4, t6, t2] >> t1
    t3 >> t5

But for strange reasons this dag can get failed status from time to time with error:

Executor LocalExecutor(parallelism=32) reported that the task instance <TaskInstance: dag_tst_tasks.t3 manual__2025-09-09T10:57:35.672635+00:00 [queued]> finished with state failed, but the task instance's state attribute is queued. Learn more: https://airflow.apache.org/docs/apache-airflow/stable/troubleshooting.html#task-state-changed-externally

In screenshots you may see that it can failed in first task or last

If i delete parallel task execution and run tasks sequentially, all tasks completed successfully.
Can someone explain why it is happening? Is it because i used default local executor and standalone version?