Z5 Display problems brightness/illumination

Hi all,

i got a problem with my display.

The brightness/illumination on display when displaying content with white background is from what I see not correct.

A certain part in the middle of my display is clearly more illuminated then the rest. But only when showing the color white.

I did the diagnosis test in the menus and here it occurred again.

Does anybody have the same issue?

Is this a display problem so I have to change my phone? Or is this just a calibration problem?

Thanks in advance:)