Intermittent delay in screen response iPhone SE

My iPhone has experienced intermittent delays in screen response over the past few months. (Not specific to iOS 11)
The symptoms include 5 second delays in typing or any touch-related activity involving the screen. Hard resets cure the problem for a while but it always returns. Sometimes after a hard reset the phone has spontaneously restarted again and during this time the battery strength will vary wildly!

After a DFU reset it still displays this behaviour but today after many hours of trial and error I wonder if it may be related to the hard, leather Apple case. In particular the proximity of the case to the Wake/Sleep button. Out of the case the phone seems ok but I haven't tried it that way for long enough to be sure.

My question is whether other users have found these cases to have such an effect on the screen.