Like the problems in iPhone 6 plus touch issues that is also one of the common problem that shows is iPhone 7 series phones.Mostly that problem causes deu to the track burnt or broken pin under audio IC.This is no dought the hardware issues that can be fixed.
@jessabethany the great inspire to cellphone repair by seeing her videos i also solved a lot of phones on that problem.
https://youtu.be/Er0oP2eUpLQ