Lightroom Classic image previews with grain are very very very bad
Problem is a little bit hard to explain so I've made a screen capture video to show what I'm talking about.
Basically since the new update images that have grain applied have VERY bad previews that make the photos look much more grainy than they actually are until you zoom in and then zoom back which corrects the problem. If however you click away from that photo and go back to it the original awful preview comes back. Take a look at the video, I hope it makes sense.
This is ultra irritating for me as I often edit hundreds of photos at once and don't zoom in and out of each one as that causes Lightroom to generate a full size preview which takes a while.