AudioKit V5 is producing no sound output from PluckedString

Question

I have the following code for AudioKit v5. The intention is to have a PitchTap for tuning and also be able to play a plucked string note. The problem is that no sound ever comes out. I have connected the PluckedString directly to the output and still no sound. Using AK v4 this worked fine. It's probably something stupid, but I can't find it. When followed in the debugger everything seems to work fine and all values are as expected.

Everything is up to date release versions AFAIK, except AK 5 which is under SPM. MacOS, XCode, iOS, 11 Pro Max simulator.

Is there perhaps an issue with AK 5 PluckedString?

    private let pluckedString : PluckedString
    private let engine = AudioEngine()
    private var pitchTap: PitchTap
    private let mixer1: Mixer
    private let mixer2: Mixer

    private let mic: AudioEngine.InputNode
    private let silence : Fader
    private let startTime = NSDate.timeIntervalSinceReferenceDate
    
    init() {
        mic = engine.input
        mixer1 = Mixer(mic)
        silence = Fader(mixer1, gain: 0)
        mixer2 = Mixer(silence)
        pitchTap = PitchTap(mic, handler: {_ , _ in })
        pluckedString = PluckedString(frequency: Float(NoteList.shared.minFreq),
                                      amplitude: 1.0)
        mixer2.addInput(pluckedString)
        engine.output = pluckedString
//      engine.output = mixer2

        self.pitchTap = PitchTap(mic, handler:
        { freq, amp in
            let t = round((NSDate.timeIntervalSinceReferenceDate-self.startTime)*100)/100
            if (amp[0] > self.ampThreshhold) {
                self.sample(freq: freq[0], amp: amp[0])
            }
        })

        do {
            try engine.start()
            akStartSucceeded = true
        } catch {
            akStartSucceeded = false
        }
    } // init

    func hammer(note: Note) -> Void {
        pluckedString.trigger(frequency: note.frequency, amplitude: 1.0)
        pluckedString.$amplitude.ramp(to: 0.0, duration: 1.5)

        print("Play frequency: " + String(note.frequency) + " Midi Note Number:" + String(note.noteNumber))
    } // hammer