Client stops working after subscribing to a topic with lots of retained messages

[gg-dim]

• [x] Bug exists Release Version 1.2.5 ( Master Branch)
• [x] Bug exists in MQTTv3 Client on Snapshot Version 1.2.6-SNAPSHOT (Develop Branch)
• [x] Bug exists in MQTTv5 Client on Snapshot Version 1.2.6-SNAPSHOT (Develop Branch)

We have a MQTT broker holding several thousands of topics with retained messages. If we try to connect and subscribe (wildcard) to a parent topic the paho client stops working. Depending on the length of the topic and the message and the network connection, the client stops working after a number of retained messages.

With Mosquitto MQTT broker somewhere in the internet it takes less than 2000 messages. With Mosquitto MQTT broker on localhost, less then 40000 messages.

I tried to find the cause, but ended up somewhere in the depths of the CommsReceiver.

[gg-dim]

It's a Mosquitto missconfiguration (max_queued_messages) and not paho issue.