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.
You will need to carefully inspect the flexes to see if there is any damage. Magnification here will help. Look for tears to the flex or any physical signs of damage. If you’re uncomfortable (or don’t want to invest in the tools necessary, consider having this looked at by an independent repair shop.