What's wrong with my service bus queue

In my chat application, I have a service bus queue created 2 years ago, which works perfectly good and very fast.

Now, I needed to create a twin application, so I created a new namespace and queue. It doesn't work. It takes 10-20 seconds to receive the message, and it does it in a random order.

I switched back to the old queue and it works perfectly again.

I've been researching for a couple of days but I don't find the reason. It's not a network problem because it happens everytime the last 2 days. Everytime I switch to the new one, it doesn't work, and switching back to the old one, it works fine.

When I created the new queue, I see that there's no more issuer name and issuer key, there's a different authorization model. So what I'm doing is:

this.client = QueueClient.CreateFromConnectionString(RoleEnvironment.GetConfigurationSettingValue("ServiceBus"), "chatmessage");

The old way was a bit more verbose

Uri namespaceAddress = ServiceBusEnvironment.CreateServiceUri("sb", baseAddress, string.Empty);

            this.namespaceManager = new NamespaceManager(namespaceAddress, TokenProvider.CreateSharedSecretTokenProvider(issuerName, issuerKey));
            this.messagingFactory = MessagingFactory.Create(namespaceAddress, TokenProvider.CreateSharedSecretTokenProvider(issuerName, issuerKey));

It's strange that, although I don't find anymore the issuer name and key in Azure portal, I still connect with those credentials.

But besides the way I create the queue client, there's no difference in the way I send and receive the messages. I simply do a Send() and Receive().

The only thing I see different is that, in azure portal, the namespace type is "messaging" for the new namespace, and "mixed" for the old namespace. But the queues have all the same properties.

Could somebody point me in any direction?

thank you.