Touch is unresponsive after powering down.

I have an iPhone 6S in for repair and it’s got water damage, I was told that the person turned the phone off immediately and put it in rice before bringing it to me.

When it arrived I opened it and cleaned out all the residue left behind and inspected it for shorts and other damage and there is none visible, I’ve even had the board out and under a microscope with no visible damage to the board either.

There is how-ever what appears to be a scorch mark on the rear facing camera as though it over heated some how but the camera works fine zooms, takes photos and videos.

I ordered a new screen because the old one was slightly cracked after the fall and the new screen is working perfectly how-ever when I turn off the iPhone for more than a couple seconds the touch is unresponsive.

But if I disconnect the battery and then reconnect it and turn it on the touch screen works, I can put the phone to sleep and leave it all day and the touch will work fine, upon losing battery power the problem repeats its self.

I have ordered a new battery, usb connector (because with that connected the phone boot loops if there is no battery connected) and camera.

What am I missing here, could there actually be a short somewhere or a broken ICU?

Any and all help appreciated.

Kind Regards

Mike