Touchscreen issue, but only in messages and Instagram

iphone 6s, since IOS 10 update, and carrying on into IOS 11 update I’ve been having an issue with the top left hand corner of the screen, but this only occurs when in messages or whilst in Instagram, all other apps work ok,

basically what it is is you tap the screen to go back and it doesn’t do anything, in more detail, in messages, you are in a conversation and tap back, it stays on the convo, puts a faint square up on the screen that says back, then it’s like when you tap it again you are on the screen with the list of all your contacts messages and you're tapping between editing the list then cancelling, even though I’m stuck in a conversation, the only way to get out of it is to kill the app and reopen, it’s a similar situation in Instagram, it won’t go back to the previous screen,

as I said earlier, all other apps work ok, the screen is the original Apple screen, with no damage to it,

so if anybody has any ideas as to what I can do to rectify this annoying issue I would be very appreciative, thanks