Celery with eventlet or gevent doesn't work properly - celery

Question

I'm running Celery using code, like this:
if __name__ == '__main__':
worker = celery.Worker()
worker.setup_defaults(
loglevel=logging.INFO,
pool='eventlet',
concurrency=500
)
worker.start()
When running Celery like this, I get the following output :
-------------- celery#some.server.com v5.2.7 (dawn-chorus)
--- ***** -----
-- ******* ---- Linux-5.10.0-19-cloud-amd64-x86_64-with-glibc2.31 2022-12-14 15:23:55
- *** --- * ---
- ** ---------- [config]
- ** ---------- .> app: __main__:0x7fdda296baf0
- ** ---------- .> transport: redis://localhost:6379/6
- ** ---------- .> results: redis://localhost:6379/6
- *** --- * --- .> concurrency: 500 (eventlet)
-- ******* ---- .> task events: OFF (enable -E to monitor tasks in this worker)
--- ***** -----
-------------- [queues]
.> celery exchange=celery(direct) key=celery
[tasks]
. task1
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b60]
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b62]
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b64]
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b67]
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b68]
Received task: task1[b248771c-6dd5-469d-bc53-eaf63c4f6b70]
But no task are executed.
If I call CTRL+C, a warm shutdown is done, and NOW, the tasks are executed
> CTRL+C
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b60] succeeded in 1.0062870910001s: None
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b62] succeeded in 1.0062870910001s: None
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b64] succeeded in 1.0062870910001s: None
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b66] succeeded in 1.0062870910001s: None
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b67] succeeded in 1.0062870910001s: None
[INFO/MainProcess] Task task1[b248771c-6dd5-469d-bc53-eaf63c4f6b68] succeeded in 1.0062870910001s: None
One thing odd I noticed here, is that the number of tasks loaded is related to the concurrency parameter. If I set it to 2, I'll have three tasks loaded, and on warm shutdown, 2 will be executed and the last one is put back in the queue.
(uh?)
Now, if I change the pool to gevent, it loads identically, but NO tasks are executed when I stop the script, instead, they are all added back to the queue.
Finally - AND THIS IS IMPORTANT - If I set the pool to prefork, it works ... perfectly fine ...
So the issue is not related to my code. Do you have any idea what is going on?
I tried to disable mingle, heartbeat and gossip with no luck.
The versions of eventlet and gevent are the latest ones of today:
eventlet : 0.33.2
gevent : 22.10.2
What is going on? Is Celery compatible with eventlet/gevent or is it just a myth?