Jagged diagonal band of different brightness

Hi all,
Just rebuilt media centre and reloaded Kodi.

Everything seems fine, but when watching videos I often get this strange band diagonally across the middle which changes the picture.

It’s very jarring, and have tried a few different settings and cannot seem to track down whats causing it.

Have searched for a solution but the symptoms are a bit too vague without knowing the specific cause.

Can anyone help?

What stupid thing have I done wrong!

Please have a look at attached screenshot (From VNC while tinkering but same on Native display)

watch gallery