Why does RPi 7" screen goes blank in Kodi

Hi

The 7" screen works fine but when running Kodi and not interacting with it the screen goes blank after about ten minutes. The Pi is still there and I can ssh into it but it is not possible to get the display back unless I perhaps unplugs the wifi sub dongle and replug it and that sometimes wakes it back up. It is not a power supply problem. I have used independent psu and when running the Pi to HDMI to a monitor all works fine.

I have the exact same behaviour on two different Pis and screens.

Any thoughts?

Thanks.