If a processor has initialization arguments, its external variables can't be resolved.

graph Mockup [[ main ]]
{
    ...
    let processorNode = WavePlayer(2);
    ...
}

processor WavePlayer (int numWaves)
{
    ...
    external soul::audio_samples::Stereo sound_1, sound_2;
    ...
}

The externals hooked up correctly in the manifest file.

"externals": {
    "WavePlayer::sound_1": "sound_1.wav",
    "WavePlayer::sound_2": "sound_2.wav" 
}

This code works fine if I remove initialization arguments (int numWaves) from the processor.