[Python] Celery raises `ValueError: not enough values to unpack (expected 3, got 0)` when...

I'm using Celery in a Django project to schedule notification tasks. When I start the Celery worker and the task runs, I get the following error:

ValueError: not enough values to unpack (expected 3, got 0)


Full traceback:

File "celery\app\trace.py", line 640, in fast_trace_task
tasks, accept, hostname = _loc
ValueError: not enough values to unpack (expected 3, got 0)


This happens when the following task is triggered:

# core/tasks.py

from celery import shared_task
from django.utils import timezone
from core.models import Notification

@shared_task
def send_scheduled_notifications():
now = timezone.now()
notifications = Notification.objects.filter(
is_read=False,
send_at__lte=now
)
for notification in notifications:
print(f"Sending notification: {notification.title}")
notification.is_read = True
notification.save()


Celery starts successfully and logs the task as received, but then immediately crashes with the error above.

My environment:

• Windows 11
• Python 3.13
• Celery 5.5.1
• Redis running locally

I’ve confirmed the task runs fine when executed manually outside Celery.

"I came across this similar question, but my error occurs in a different version of Celery and the task seems structured correctly."
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