I'm pretty convinced it's a hardware issue at this point. I want to replace my 12.9" 2nd Gen. but I don't know what to replace it with (iPad-wise) because it seems that all the newer models are also demonstrating this issue.
My spouse has a 10.5" iPad Pro 2nd Gen. and it works great--no touch issues and no white spot. There's also another family member with the iPad 6th Gen. and it works great as well. My iPad Mini 4 works. My 12.9" iPad though, sucks.
I can't bring myself to replace it because I simply don't know that this isn't going to happen again, which it probably will. I think, for me, I'm done with Apple products until these issues are addressed.
Can relate to this. The thing to remember though is that those of us experiencing the issue are a small subset of the user base. Still . . the fact that the issue exists in the new generation of pros is a concern for those of us with experience with the issue, particularly given the fact that upgrading to the next generation means another large investment in the device and accessories.