Many of my .psd thumbnails display badly, running Sequoia 15.4.1

Hi all!

I'm having a big problem with some .psd thumbnails displaying weirdly now that I've installed Sequoia. I'm on a MacBook Pro 14-inch 2021 M1 running Sequoia 15.4.1. The thumbnails look very strange. Many have white grid overlays that don't exist in the document, others are plain white, others show every single layer in the document in a mishmash. Some are OK, however, I think it may be file-size linked or maybe linked to the number of layers? My old file thumbnails look fine but the moment I open or use a file some of the thumbnails regenerate and look terrible. In case it means anything, I also can't use the spacebar preview to see what's in those files or compare them as of Sequoia 15.4.1. This is so bad for my workflow as a graphic artist that I may downgrade my Mac OS (already tried downgrading Photoshop and that didn't help even when resaving files.)

I have reported it as a bug to Feedback as well but hope someone here has a solution. Thanks for any help!