Interesting. I had the same exact issue. I attached a photo of it when it was happening at a lesser extent (it was very intermittent) Apple replaced it no problem once I was able to reproduce it for them. Luckily it had a full on stripe fest in front of the "Genius".
As far as if they have spares. I went to the Apple Store in Grand Centeral in NYC and he said they had 3 of my model available for spares (16GB Vz 6 Plus)
As far as if they have spares. I went to the Apple Store in Grand Centeral in NYC and he said they had 3 of my model available for spares (16GB Vz 6 Plus)