First, I am assuming that you tried on the new digitizers without gluing them or pushing them hard in place? (To rule out a creased digitizer cable due to improper installation).
Second, did the iPad show any signs of drop when it came back?
Any sign of liquid damage?
Note: did you try a restore? (Asking if you did, not suggesting that you do).
After ruling out the above, I'd use a magnifying glass to look at the touch-screen connectors on the logic board to see if:
- The retaining flaps are missing, broken, displaced;
- The connector is damaged, any pins are broken; you could even test continuity between the connector and logic board;
- Any components around them are missing or broken.
Have a look and let us know what you see. We can take it from there.