Weird pixelation / colors in cinematics in-game

Hi gang - I have a RTX 4090. If I watch the cinematics for World of Warcraft in YouTube, they look perfect on my hdr monitor (either with HDR on or off) - nice blacks, colors, perfect

However, if I watch the same cinematics in-game I get very odd pixelation

I have tried this with HDR on and off, resetting the video settings within WoW. Any idea what might be causing this?