MIDI keyboard volume keeps automatically going to zero

Hi all,

I have no desire to record in GarageBand, I simply want my MIDI keyboard (which has no speakers) to run through GarageBand so it sounds nice coming through my desktop speakers. I've connected a MIDI keyboard to my iPhone 6s using an adapter. I select 'Smart Piano', grand piano setting and start playing. All sounds good and is working fine, then after a minute or so the track volume goes down to zero and I cannot hear the piano. If I open track settings I see the track volume is at zero. I move it up to full and I can play again. Then after a minute or so it slides back down to zero.

I'm using a Nektar MIDI keyboard. It works perfectly fine when I'm using Simply Piano on the iPhone 6s – it's only fading out when using GarageBand.

Hoping someone can help me. Thanks in advance!