Python class variable usage across thread have different value

Question

I'm getting confused about class variable access through multi-thread. I'm in a django application and I initialize a class at server startups to inject some configuration. Then on user requests I call some method on that class but the config is None.

class SharedService:
    _queue_name = None

    @staticmethod
    def config(queue_name=None):
        if queue_name:
            SharedService._queue_name = queue_name
        print(SharedService._queue_name)    # this print the "alert"

    @staticmethod
    def send_message(data):
        print(SharedService._queue_name)    # this print None should print "alert"

if usefull in the django settings class loaded at startup I do:

SharedService.config(queue_name="alert")

and in the user endpoint I just call:

SharedService.send_message("blabla")

I'm sure it did work previously, but we did update to python 3.10 and django 3.2 recently and might be related (or not!)