One-off Tasks Executed Multiple Times After Celery Beat Restart

[smalyu]

Issue Description

One-off tasks in django-celery-beat are executed multiple times if Celery Beat is restarted shortly after the task runs.

---

Steps to Reproduce

1. Create a one-off task (one_off=True) scheduled to run at a specific time.
2. Start Celery and Celery Beat, wait for the task to execute.
3. Verify the task has run.
4. Restart Celery Beat within 10 seconds after the task’s execution.
5. Observe that the task runs again after the restart.

---

Expected Behavior

• One-off tasks should only execute once, even if Celery Beat is restarted shortly after their execution.

---

Actual Behavior

• The one-off task is executed again if Celery Beat is restarted within a short time after its initial execution. However, if several minutes pass before restarting, the task does not run again.

---

Versions

• celery==5.4.0
• django-celery-beat==2.7.0