Incoming call display delays 2-3 seconds after screen replacement

Hello folks,

A client of mine called me a few days after I replaced his iPhone 6 screen (no assambly, al sensors where moved from the old screen).

He says that since I changed the screen every time he get's an incoming call he has to wait about 2-3 seconds before the screen lights up and he is able to reply. Can this be related to anything I did wrong during the replacement?