drywetmidi: Playback produces unexpected results in Unity

I’ve integrated DWM into my Unity project (2019.1.0f2) for MIDI file playback and parsing. I’ve called playback.Start() and the MIDI file will not play. I have tried several MIDI files and nothing will play.

// Use the first available OutputDevice (Microsoft GS Wavetable Synth)
var outputDevice = OutputDevice.GetAll().ToArray()[0];
// The MIDI file is copied to this location earlier
var playback = MidiFile.Read(Application.dataPath + @"/Scripts/in.mid").GetPlayback(outputDevice);

Later, in a coroutine (so the MIDI file starts playing at a specific time):

playback.Start();

Playback doesn’t want to start, even on the main thread.

Also, playback.Play() works, but it freezes the thread which I don’t want, and it also drops a lot of notes, even on really simple MIDI files.

No exceptions are thrown.

What am I missing? And is there some fix to the dropped notes?