I would like to bump this one as I suspect I have the same or a similiar issue.. I'm trying to implement user presets, and when calling saveUserPreset: I get no error, but it also doesn't update the userPresets property, and I get no notification of any sort as per the documentation (https://developer.apple.com/documentation/audiotoolbox/audio_unit_v3_plug-ins/incorporating_audio_effects_and_instruments?language=objc). Essentially it behaves more like it just fails silently. I've downloaded the demo project on the link above, and when I run that iOS app, selecting the AUv3Filter demo component I can save user presets, so technically I can see that it is possible. However, I cannot for the life of me find what it is that specifically makes it work, as there are no custom implementations of saveUserPreset. I am starting to suspect it's a configuration issue, but I can't figure it out. Any ideas at all would be helpful.. :)