How long have you owned this phone? If it is a short time, you can send it back to the retailer for a replacement. If you have used it for a long time, then did you ever drop it and try to fix it by yourself? If yes, the adhesive gluing the screen and the frame may not be so strong enough to stick on the right way. And just like Candido said, you have to remove the disaply again and replace with the good quality adhesive. Here is how to replace LG G4 screen: https://www.youtube.com/watch?v=ZRgQ2rI9XVE