I have a 7 inch touchscreen which has been working fine over the last few years but recently it has a dead zone across the centre (full width, landscape orientation). It works fine at the top 25% and the bottom 40% approximately.
I have checked the connections and they all seem OK - any suggestions please to get it to work properly over the whole screen?
I first noticed it using PiCorePlayer but have also confirmed the symptoms using Raspbian latest version. Presumably it is a hardware problem?
Based on your description, it sounds like the screen has probably died from some kind of physical fault. The only way I can think of to ensure it may not be is to try it with a different RPi, but that seems like a long shot.
I'd suggest that accepting that the parrot is no more.
I'm experiencing the same problem using this display on ArchLinux-ARM.
I was working fine today till evening.
After dinner I perform a system update and now the touchscreen doesn't work correctly. I got a dead zone (only for the touch functionality) in the top side of the screen. I definitely cannot touch on the top side of the screen.
I got other issues also in libinput inside Xorg. I think that it could be an upgrade problem (pointing to Waylan or Weston or libinput) - I know that with evdev I got no problem at all before, but something changes after upgrade, and libinput is the future (evdev will be deprecated)...
I have noticed the same problem in about 10% the units I've seen. After more than a year the touch area gets a dead zone that eventually grows until it's all gone. We use the same software on all units, so, it's most likely some kind of electrical issue.