Hi JwEaFgFnr,
I have a 6+, iOS 9.0.2 (upgrading my iOS CAUSED this problem, 9.1 doesn't seem to FIX the problem, so I see no reason to risk things getting worse with 9.1). NO screen protector. I did use a case, but have stopped using it because it felt like it made things worse, but the intermittent nature of this problem makes it extremely difficult to associate root causes. It FEELS like the touchscreen is "seeing" incorrect touches. I also went to Settings: General: Accessibility: Touch Accomodations: Hold Duration, turned it on, set to .35 seconds. (I'm still not entirely clear whether this is active, since I haven't enabled Touch Accomodations, but it feels like it helps.)
Here are my symptoms:
+ Touchscreen does not respond at all to my inputs. This happens perhaps several times a week at this point for me. Generally, if I leave the phone alone, it returns to normal after a few minutes.
+ Sometimes, touchscreen does not respond to my inputs AND it accepts phantom touches/input. If a keyboard is loaded at that time, it types by itself. This sounds like it matches what other people have reported with strange lines being drawn. I _believe_ that this has happened much less after I set up the hold duration.
+ Vertical lines on the right side of my screen, a little like pinstripes, but of varying width, intermittently. Hard to see, especially when I have photos as wallpaper - easier to see if your wallpaper is set to a black image. It feels like there are ALWAYS lines displayed when the phone is misbehaving, but I do see lines sometimes when it ISN'T misbehaving. No lines right now.
+ I've had phone calls dropped during these problems. I've also had phone calls I could not answer - you need to swipe to answer. I've theorized that a headset might be a workaround in such cases, since I can answer by pressing a button instead of swiping.
I _used_ to do a hard reset to fix the problem, but I'm simply leaving the phone alone now, and it recovers.
These problems started after I upgraded to 9.0. I had absolutely no issues with iOS 8.x regarding the touchscreen. I have been using iPhones since the 3GS, and have not experienced problems at this level before.
I've definitely learned a lesson, to not upgrade to a new iOS unless a) there's specific functionality I really want/need, b) it's been around long enough to really be stable (though it's not clear to me I would learn about this specific problem without actually encountering it, it doesn't seem very well publicized), and c) I'm ready to have ongoing issues without getting too upset.
By the way, I did go to the Genius Bar, and they said absolutely nothing was wrong with my phone. There's no Genius Bar where I live, so I can't easily go for another appointment - I was visiting Seattle recently when I stopped by - but I would definitely be willing for them to try to replace my phone completely, if we thought that would help. It's clear to me that resetting it does NOT help, since so many other people have tried that and it didn't work. And it SOUNDS like someone with a 6s is also experiencing this! I thought it would be limited to older phones.
Hope some of this helps identify common symptoms and possible solutions!