Adobe Bridge uses Camera Raw to generate HQ thumbnails and previews (unless you opt to use embedded previews). This is a pretty useful feature because you immediately see the effects of any raw settings and crops applied to thumbnails and previews in Bridge.
It's never been perfect, and there's always been some strange artefacts. But mostly it's been a very minor problem.
In recent months, I have noticed a few anomalies in both Bridge previews and alt-slider visualisations. Both seem blocky/pixelated, and previews colours can look off, especially in darker images. Here's an extreme case:
Indeed, when you first load one such image into Camera Raw, it looks like this while the rendering preview builds.
Eventually, the image looks like this:
I can fix this by clearing the Camera Raw cache, and then purging the preview cache. However, as soon as I load the image into Camera Raw again, the ugly preview is back. This seems to happen regardless of GPU support settings.
It's almost like the previews have become posterized.
If the problems keeps cropping up even after you clear and purge the caches, maybe it's a video driver issue?
ON EDIT: Even if you disable GPU support, that still doesn't leave the video driver faultless. All the GPU setting does (if I recall) is enable acceleration.
The fact that the Bridge preview is fine until Camera Raw opens the file (and therefore caches the CR preview) suggests to me that it's something to do with the Camera Raw cache.
The Bridge preview is okay once the Camera Raw cache is purged, and the HQ preview is regenerated. Obviously, this is no use once you make any alterations in Camera Raw.
Actually, it's not a big deal, because it seems to affect darker images a lot more than lighter ones. In fact, it seems to be worse the higher the Shadows setting.