(Unit test is attached to prove the case)
Given 3 brokers A, B and C.
Each broker is connected to the others by a network bridge (so we have 3 brokers that are connected to each other)
The networkTTL is 2 on all network connectors.
Start broker A and B
Subscribe consumer on A
Start Broker C
Stop Broker B
Publish message to C
The consumer that is subscribed on A receives the message
Sometimes it works and sometimes the consumer does not receive the message.
From my understanding the problem appears since a broker subscribes as a consumer to other brokers only when there is a consumer that subscribed to this broker, but it does not try to renew subscription to other brokers when some (another) broker in its network fails (or stopped).
So we see the following situation:
Client subscribed on topic X on A, A subscribed on topic X on B, B subscribed on topic X on C
When we stop B, A does not subscribe on topic X on C and the message of topic X cannot pass from C to A.
This BUG does not occur when networkTTL is 1 because subscription route in a network will be not be greater then 2