Looks like the new iPhone 7 Plus too has some hardware problems. As per reports the problems are related to the phone's camera hardware.
A post on Reddit titled iPhone 7 Plus Cameras Are Dying states :
‘I opened up the camera app only to be met with a black image preview, sometimes I can get an image however it's either tinted green or purple and was once accompanied by a screen stating 'Emergency iPhone needs to cool down' when the handset wasn’t even slightly warm.’
Many other users too are experiencing similar problems. SOme of them had had their device replaced at the Apple store due to a ‘hardware fault’, while a few have had their iPhones repaired at the Genius bar by the installation of a new camera module.
Since Apple is replacing the iPhones, it means the company is aware of the fault although it hasn't issued any public statement about the same
So, if you are one of those few unfortunate ones who is facing a problem with the camera, go to the nearest Apple store to get a replacement or get it repaired at the Genius bar. However, the former would be a better choice.