Certain queues are not connecting and we see the following in the hub.log
"Subscribe error: replacing current subscriber not permitted, denying request"
hub 7.x and above
Two hub's are trying to subscribe to the same queue. For example two get queues are trying to connect to the same attach queue.
Get/Attach queues have a one to one relationship. You will need to disable the extraneous get queue to resolve this problem.
Hub to Hub Queues