I think your touchscreen is broken. I had the same issue with my Z3 Compact. Started with the 3 buttons "Back, Home and Recent Apps". After That the upper edge went dead, so swiping down for notifications and quick setting didn't work no more. There is a work around with apps like Simple Buttons were you can put the buttons on any side of the screen. This works perfect because these buttons are from a third party app and therefore (I believe) placed on a different layer. Because, why is the screen working properly in apps, while the native buttons stop working?
Software repair or reinstalling doesn't resolve the problem.
The other solution is to the get your phone to a repair center. I think you will end up with this scenario. That's why I ended up with a X Compact. As a replacement for my beloved Z3 Compact.
On this forum, but in the Z3 Compact section, there are several threads about this issue.
Good luck.