The best solution is Sony's Authorized Service Centre or other Electronic Service that repairs sony's devices.
If the device is on warranty and there are no Services available in a region, You can try to replace/return it in the place you bought it from.
These are the only things that comes to my mind, there is no magic solution and I'm 80% sure if reinstalling android won't change anything it's a faulty unit, not software issue.
My Z2 is healthy 100%, all the updates istalled, so it's nothing like a global system problem just some faulty devices on market.
