Watching Spider-Noir on my QM8K and I'm noticing issues with varying grayscale?

I started watching Spider-Noir in black & white last night on my 85" QM8K. I'm noticing that the grayscale(?) seems to change randomly between a true gray, to a brownish gray while watching. It happens in a quick flash, so it's very noticeable.

Anyone else noticing this?

And sorry if I'm describing the issue poorly, or not using the correct terminology.