Just a thought …. have you got something else connected to the iPad air via Bluetooth?
the reason I ask is that from my experimenting any 64bit iOS device (iPhone 5S,iPad Air , iPad Mini 2 onwards) seems to allow two H9's simultaneously wheras a 32bit device seems to allow 3 simultaneous connections.
I discovered this when I first got an iPad Air and replicated it with my iphone 5S, then an iPad Air 2 and an iPhone 6 …. all seem to allow only 2 Bluetooth devices to connect.
I then tried the same experiments on my daughter and wife's iPad Minis and iPhone 5's (2 x iPhone 5 … NOT iPhone 5S) … they all accepted 3 H9's
Given that all the devices were running the same level of iOS … I would suggest it it was something to do with a change in hardware when the 64 bit platform came in or something in the 64 bit code??
But I have not seen any issue with only being able to connect only 1 H9 at a time … only when I had another bluetooth device connected at the same time.
Not sure if this answers your question?