I have a 6 plus. I broke the screen a few months ago, so they replaced it with a brand new 6 plus (hence new battery). It is very slow in much the same way th

I have a 6 plus. I broke the screen a few months ago, so they replaced it with a brand new 6 plus (hence new battery). It is very slow in much the same way that many other people describe -- it will just pause for a long time (a minute or more) in some weird stuck state. The old phone that I broke had the same problem. I have the minimum apps installed, and background refresh disabled. My wife and mother both have 6 pluses, which exhibit the same weird long pause slowdown behavior. After trial and error, the best hack to get around it is: (1) when it happens, immediately turn the phone off and on with the upper right power button, then (2) immediately after the phone turns back on, close all running or suspended apps. If you don't do (1), then you're just completely stuck for a long time. I've had this problem before and after iOS 11, and with my new and old phones.