Problem with subscribe ESP got hang

[dogrocker]

Hello I have problem with subscribe when it received data from subscribe.

if(mqtt_connected) {
    client.subscribe("topic/setting/+")
    // payload will be `topica/a`
}

void callback(const MQTT::Publish& pub) {
   String topic = pub.topic();
   String data = pub.payload_string();
    // I cut string with `setting` on topic
    if (receive topic == "setting") {
        client.subscribe(payload);
    }
}

and I use client to subscribe with retained like.

topic = topic/setting/1
payload = topica/a
retained

topic = topic/setting/2
payload = topicb/b
retained

       // so when esp boot it will be 3 subscribe
       // 1.topic/setting/+

       this 2 will subscribe in if condition.
       // 2.topica/a
       // 3.topicb/b

NOW I got esp hang. if I set retain more than one topic.

but If I use retain with one topic like.

topic = topic/setting/1
payload = topica/a
retained

my esp not hang.

don't know what the problem are.