I struggled with iPads for a long time. Here's what I suggest. After removing your digitizer, use a metal sanding material(think scotch-brite) soaked in 99% isopropyl and scrub the frame surface until it's completely smooth. Then, I use a very high quality tape to apply it, I will link it below. Better adhesive is really the answer. I also find I get better results when I apply the adhesive to the frame first.
After laying down your digitizer, use some plastic clamps and clamp the 4 corners as well as one in the middle on the top and side. Two clamps will go on either side of the home button. Once it's under pressure, heat the screen and allow it to rest and cool for about 10 minutes. I haven't had a single issue after using this method. Also make sure you're getting your digitizer cables folded right. Hope this helps!