I found a Few Glitches in the Story Line and in normal Game play, Please note this CONTAINS SPOILERS ON THE ENDING
Zombie Kate ~
After you do the Mission where you must Chose Between the Deal or go kill Dimitri, go kill Dimitri and after i completed it go to the wedding with Kate. Kate gets Gunned down by Jimmy. So After awhile I got a Phone from a Unknown Caller, In this call it said: Hi niko, i thought you were Dead, wanna Hang out? which later the Phone Showed me this: do you want to go on a Date with Kate? even though she was Gunned down, so i accepted the Date after the date ended i got a Call from Packie mourning the Loss of Kate which i just dated. idk if this will happen to anyone Else but it happened to me.