Random black screen with new TV

Hi all,

Upgraded from 55 LG OLED B7 to 65 C9 previously the latest coreelec worked flawlessly on a 912 box.

Now all of a sudden I get random black screens playing some content. Tonight after stopping and starting some SD content it went black can hear sound but no picture, reboot and get a black screen after the coreelec splash screen, had to switch input on the AVR to somthing else then back again for it to work again.

After a couple of reboots was able to finish watching the show then when I stopped it I got another black screen instead of the menu.

Any ideas?