If streams shutdown is initiated during state restore (e.g. an uncaught exception is thrown) streams will not shut down until all stores are first finished restoring.
As restore progresses, stream threads appear to be taken out of service as part of the shutdown sequence, causing rebalancing of tasks. This compounds the problem by slowing down the restore process even further, since the remaining threads now have to also restore the reassigned tasks before they can shut down.
A more severe issue is that if there is a new rebalance triggered during the end of the waitingSync phase (e.g. due to a new member joining the group, or some members timed out the SyncGroup response), then some consumer clients of the group may already proceed with the onPartitionsAssigned and blocked on trying to grab the file dir lock not yet released from other clients, while the other clients holding the lock are consistently re-sending JoinGroup requests while the rebalance cannot be completed because the clients blocked on the file dir lock will not be kicked out of the group as its heartbeat thread has been consistently sending HBRequest. Hence this is a deadlock caused by not releasing the file dir locks in task suspension.