Chosen Solution
I know there’s plenty about this already, but I think this is slightly different. This one self selects etc after 5 minutes of use???? All the tape has been transferred over to the new digitiser so there is no gold contacts showing to touch on the frame. The flex cable is tucked up inside the small gap and not pinched between the glass and frame. I can’t think of what else it could be, especially when it’s after 5 minutes of use (Possibly heat related? )
It could be an issue with the board. But then it could be something else. You’d better rule out digitizer and insulation issues first. To do that, open the iPad (flip out the digitizer), keep everything connected, and test. If issue is gone, you did not transfer the black tape properly (I’d also insulate the magnets), etc. If issue remains, disconnect the battery, press power button for 15 seconds, connect and test. If still no change, put back the old digitizer, without gluing it, and test. Let us know what you find out. By the way, why did you have to change the touch screen in the first place?