Audio Units v3 iOS: Instantiate AVAudioUnit

I have a real-time audio unit which is defined in a Objective C class. When I instantiate the class with AVAudioUnit.instantiate(...) everything works fine, but if I instanitate a second object with that class, the result sounds like choped. Copying the class definition, i.e. creating a second identical class Objective C class definition and instatiating this one works as expected. How do I instaniate the same class definition more than once?