The container calls commitSync() unconditionally in commitAcknowledgments():

private void commitAcknowledgments() {
    try {
        this.consumer.commitSync();
    }
    catch (Exception e) {
        this.logger.error(e, "Failed to commit acknowledgments");
    }
}

ShareConsumer also has commitAsync() but it is not used. Add a ContainerProperties.setSyncShareCommits(boolean) flag (default true) so users can opt into async commits when slight ack-durability lag is acceptable.