The iPhone 7/8 series have a very inconvenient bend on the Home Button flex. It’s really easy to tear the flex, either near the logic board connector or at the 90 degree bend before it sneaks underneath the LCD heat shield. You have to be careful when you lift the screen off the first time but also anytime the flexes are connected and you have the device open.
The other area that is easily damaged is the connector on the Home Button itself and the opposite connector on the short flex that runs underneath the heat shield.
The long and short of it is that there are multiple failure points. Take a really close look, use magnification if necessary to see if there is any damage at all.