AVAudioEngine warning: "deprecated Carbon Component Manager for hosting Audio Units"

Question

I'm writing my first audio app for Mac, which loads an external audio unit and uses it to play sound through an instance of AVAudioEngine, and I've been seeing this warning:

WARNING: 140: This application, or a library it uses, is using the deprecated Carbon Component Manager for hosting Audio Units. Support for this will be removed in a future release. Also, this makes the host incompatible with version 3 audio units. Please transition to the API's in AudioComponent.h.

I've already transitioned from using AVAudioUnitComponents to AudioComponents (now accessed via this api) which I expected would solve this issue, but I'm still seeing this warning when I call start() on my engine.

Any ideas what's going wrong here? As far as I can tell, I'm no longer using deprecated APIs. Is it possible that AVAudioEngine is using deprecated APIs under the hood?

Here's a snippet from the code I'm working with. I'm calling selectInstrument with a description I've retrieved using the AudioComponents API.

public func selectInstrument(withDescription description: AudioComponentDescription, callback: @escaping SelectInstrumentCallback) {
    AVAudioUnit.instantiate(with: description, options: []) { avAudioUnit, error in
        guard let unit = avAudioUnit else {
            callback(nil)
            return
        }

        self.disconnectCurrent()
        self.connect(unit: unit)

        unit.auAudioUnit.requestViewController { viewController in
            callback(viewController)
        }
    }
}

private func disconnectCurrent() {
    guard let current = currentInstrument else { return }
    self.engine.disconnectNodeInput(engine.mainMixerNode)
    self.engine.detach(current)
    self.currentInstrument = nil
    self.engine.stop()
}

private func connect(unit: AVAudioUnit) {
    let hardwareFormat = self.engine.outputNode.outputFormat(forBus: 0)
    self.engine.connect(self.engine.mainMixerNode, to: self.engine.outputNode, format: hardwareFormat)
    self.engine.attach(unit)
    do {
        try ExceptionCatcher.catchException {
            let stereoFormat = AVAudioFormat(standardFormatWithSampleRate: hardwareFormat.sampleRate, channels: 2)
            self.engine.connect(unit, to: self.engine.mainMixerNode, format: stereoFormat)
        }
    } catch {
        let monoFormat = AVAudioFormat(standardFormatWithSampleRate: hardwareFormat.sampleRate, channels: 1)
        self.engine.connect(unit, to: self.engine.mainMixerNode, format: monoFormat)
    }

    unit.auAudioUnit.contextName = "Running in AU host demo app"
    self.currentInstrument = unit

    do {
        // Carbon Component Manager warning issued here:
        try self.engine.start()
    } catch {
        print("Failed to start engine")
    }
}

Thanks for your help!