Phone screen shuts off several days after screen replacement

Following the screen repair of an Iphone 6, iphone 5s, iphone 6 plus, and iphone 6s the screens appear to work perfectly; however, the owners of each of these phones had issues several days and in most of the phones several weeks following the repair. The 5s, 6, 6 plus all shut off and wouldn't power on while the 6s became unresponsive to touch. I have repaired many phones before this without ever having this issue. Is it something I may have damaged during the repair, bad screens, or just an issue with the phone that a screen repair is guaranteed to fail because of some other issue with their devices?

Any insight on the matter is greatly appreciated