I had the exact same problem the other week.
For me it wouldn't lock even with the glass away from the frame, so knew it wasn't a grounding issue. Plugged another digitiser in, and it worked.
As I need to practice my soldering, I just sent the defective part back.
If you have covered all the contacts on this new screen to know it can't be this, and you still have the original screen, just plug it in to eliminate the part/ipad at fault.
someone mentioned before it's something to do with sleep function which goes through the home flex cable.
Good luck.