When trying to send a true to a "devicePairingUserConfirmationRequest" (in IOBluetoothDevicePairDelegate), there is no command sent via the HCI controller, i.e. when running PacketLogger there is no User Confirmation Request Reply. This causes a timeout and the a Simple Pairing Complete and Authentication Failure.
This within itself is a strange behaviour (since the replyUserConfirmation function is being called), but if I send a replyPINCode, it magically works. This is behaviour was seen using both swift and objective-c cli and a simple swift APP.
Also, if I connect to the device from the bluetooth settings page, the device pair without any problem (although when capturing system logs using Instruments, the pairing logic is completely different, using its own functions and API calls).