As a professional iPad refurbisher I can tell you that ghost typing on a 9th Gen. (or 7th or 8th) in my experience has caused by digitizers that are not properly seated on the motherboard FPC connectors, (more likely on the one in the left).
The other causes can be bent or missing pins on either of those FPC connectors which can be caused by pressing too hard when trying to seat one or both connectors,
The third possibility is a defect in the digitizer itself other than either of the connectors.