It worked for me a few times then stopped and haven't worked ever since. Finally I've just disabled it since I don't have much use for it anyway (it doesn't have many cards in my country).
Mine works on all screens and when the phone is locked as well. I did have to turn off S voice in order for it to work when the screen is off though. I'm stock on Sprint 5.0.1
I had the same problem after I updated to Lollipop. Nothing I tried fixed the problem and I tried ALL the suggestions. So I just downloaded Google Now launcher and made it my default launcher and everything is just fine again before Lollipop.