Timestamping in AUv3 MIDI plug-in

I am trying to understand how timestamping works for an AUv3 MIDI plug-in of type "aumi", where the plug-in sends MIDI events to a host. I cache the MIDIOutputEventBlockand the transportStateBlock properties into _outputEventBlock and _transportStateBlock in the allocateRenderResourcesAndReturnError method and use them in the internalRenderBlockmethod:

Code Block 
- (AUInternalRenderBlock)internalRenderBlock {
    
    // Capture in locals to avoid Obj-C member lookups. If "self" is captured in render, we're doing it wrong. See sample code.
  
    return ^AUAudioUnitStatus(AudioUnitRenderActionFlags *actionFlags, const AudioTimeStamp *timestamp, AVAudioFrameCount frameCount, NSInteger outputBusNumber, AudioBufferList *outputData, const AURenderEvent *realtimeEventListHead, AURenderPullInputBlock pullInputBlock) {
        // Transport State
        if (_transportStateBlock) {
            AUHostTransportStateFlags transportStateFlags;
            _transportStateBlock(&transportStateFlags, nil, nil, nil);
            
            if (transportStateFlags & AUHostTransportStateMoving) {
                if (!playedOnce) {
                    // NOTE On!
                    unsigned char dataOn[] = {0x90,69,96};
                    _outputEventBlock(timestamp->mSampleTime, 0, 3, dataOn);
                    playedOnce = YES;
                    
                    // NOTE Off!
                    unsigned char dataOff[] = {0x80,69,0};
                    _outputEventBlock(timestamp->mSampleTime+96000, 0, 3, dataOff);
                }
            } 
            else {
                
                playedOnce = NO;
                
            }
        }
        
        return noErr;
    };
}

What this code is meant to do is to play the A4 note in a synthesizer at the host for 2 seconds (the sampling rate is 48KHz). What I get is a click sound. Experimenting some, I have tried delaying the start of the note on MIDI event by offsetting the _outputEventBlock AUEventSampleTime, but it plays the click sound as soon as the play button is pressed on the host.

Now, if I change the code to generate the note off MIDI event when the _transportStateFlags are indicating the state is "not moving" instead, then the note plays as soon as the play button is pressed and stops when the pause button is pressed, which would be the correct behavior. This tells me that my understanding of the AUEventSampleTime property in MIDIOutputEventBlock is flawed and that it cannot be used to schedule MIDI events for the host by adding offsets to it.

I see that there is another property scheduleMIDIEventBlock, and tried using this property instead but when I use it, there isn't any sound played.

Any clarification of how this all works would be greatly appreciated.