I had an ebay ipad4 wifi exhibiting extensive ghost/phantom touches, so bad you can’t log in, magnifier feature was the most common activated, but general mayhem.
I also assumed digitizer, but my first replacement (ifixit digitizer) showed the exact same issues. Bodydid not appear warped, no bent corners etc. My only clue was I could sometimes get it to behave before pressing the digitizer down onto the adhesive. I went in circles for a while, tried everything suggested everywhere. Kapton tape over areas of the digitizer frame, reseating and cleaning contacts, checking cable management for possible grounding. Nothing was working!
Then, I tried working my way around with the ipad awake while I attempted to seal the digitizer… the phantom touches appeared on the left side as I pressed down, not near the digitizer ribbon cable, more in the center. Curious!
One of the things I tried previously was to tighten any screws in the chassis I could find. However I neglected the small pairs of screws (PH000) that run down the left side in the aluminum frame that surrounds the display. A few of these accepted another turn or two (with some force).
As I resealed the last time the ghost touch was gone! Of course my seal sucks now due to the adhesive getting mangled multiple times in successive attempts, and it’s only been a few hours, so don’t know if they will return.
My suspicion is there is a very very small tolerance for any bend in this part of the internal framing that causes it to approach the digitizer more than it should? That is my best guess, but it seems to have solved it for me. I don’t think this will be the solution for everyone, as there seem to be multiple vectors for getting ghost touches as a problem.