Given an outstanding consumer transaction and failover transport recovery. On recovery, messages are redispatched by the broker once the connection, sessions and producers/consumers and transactions are replayed. Redispatch may not dispatch the same messages to the same consumers atm. In the case that a client transaction cannot be recreated it should fail with a TransactionRolledBackException. The failure indicates that the messages the session wants to ack have not again been redispatched so their receipt cannot be committed. The messages in question will have been redelivered to another consumer.
Likewise in a rollback, in this case there is a warn message to the effect that the rolled back messages may not all be included in the rollback. It that they may not have been redispatched. The unordered redelivery semantics after a session rollback ensure that this error does not need to propagate up to the client.