Thanks for following up on this old question. I agree completely with being defensive. I was just curious if I had missed something.

Bingo!

Thanks for the reply. Good to know I'm not alone. Curious too that our packets are quite close in size.

Hi Gene. Apologies for the delay --I just saw this. The packeList comes from the argument given to the closure I give to MIDIInputPortCreateWithBlock -- I call packetList.pointee to get a MIDIPacketList which is what I work on in the code above. The issue only manifests when I quickly and repeatedly press down on a lot of keys, generating a lot of MIDI traffic.