Not receiving PubNub messages when the user is not actively interacting with any channel

Question

When two clients are subscribed to the same channel, they communicate as expected. However, if I don't perform any kind of activity, such as not sending a new message for an hour, an issue arises. These two old clients can send and receive messages, which is expected. But if I reconnect one of these two old clients or add a new client to the same channel, the old client(s) that were created in the beginning do not receive messages sent by the new client. However, when an old client sends a message, the new client receives all of those messages.

My Client was created with this configuration:

let config = {
    publishKey: pubKey,
    subscribeKey: subKey,
    userId: userId,
    ssl: true,
    presenceTimeout: 300,
    heartbeatInterval: 60,
    heartbeatTimeout: 120,
    keepAlive: true,
    restore: true,
    autoNetworkDetection: true,
    wildcardSubscribe: true,
    leaveOnUnsubscribe: true
};

let client = new PubNub(config);

I was subscribing using this:

client.subscribe({
    channels: ["myChannelName"],
    timeout: 1200
});

I was expecting that the old and new clients should communicate with each other without any issues, as they are connected to the same channel.

But how can I achieve these?