Regular 6 Plus user reporting in here (don't have my 6s Plus yet). I generally don't have any issues getting Control Centre to pop up on my phone aside from when I'm in an app or two. I have been in apps where I tried to pull up the CC and I get the tab after the first swipe and when I swipe a second time the tab just goes away, but even then I only run into it often in one specific game that I play all the time. Most other apps I use on a fairly regular basis, I don't have issues with.