iPhone 6+ with flicker at top and non-responsive touch

I bought a 6+ a year ago and upgraded to iOS 9 without any incidents. Over the past 6-7 days, I've noticed that at random intervals there is a flicker at the top of my screen. I'm not sure how many lines it takes up, but it's there. I've also noticed that all of a sudden my screen isn't responsive to my touch, or it's way off line. So for example, I'll press an icon on the bottom row and it may lag 5-10 seconds (maybe longer?) and then the icon on my 2nd row will be selected.

I took it to the Apple store and they ran a screen diagnostic on it and couldn't find anything wrong with it.

Anybody else see this problem?

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Sounds like a digitizer issue of some sort. Have you dropped your device?

Surprised the Apple Store didn't find this an issue. I would take it in again as this is not normal in my opinion.

No, haven't dropped device. The screen is no more or less dirty than it was a week ago as well.

Originally I thought this was an issue with upgrading to iOS 9, but I did that about a month ago or so ... and this just started happening in the last week.