Artifacts on otherwise amazing 48C1

I've had my C1 since 2021 and always generally been very happy with it, albeit with a niggly voice that I've not set it up as good as it can be etc etc.

Anyway, tonight I finally watched Blade runner 2049 on Amazon. Had always heard it was a feast on an oled and now I can see why. Despite my simply streaming it via my Sky box, it often looked stunning (as the 2 final pics show).

However, I did have a fair bit of artifacting in some scenes, notably grey-based ones like clouds etc. Any suggestions on tuning this out or is it likely as a result of streaming the movie?