Since updating to 21.1.0, I've noticed something weird - when opening an image, the thumbnail for the Background layer is ok, but as soon as I create an empty layer, or duplicate the layer, or just turn the Background layer into a regular layer, then the layer thumbnails appear "contracted".
This image shows how the Layers palette (and more specifically, the layer thumbnails) looks like when opening a new document, and how it looks like just after clicking the "new layer" button:
Anyone else experiencing the same? I'm using Windows 10, by the way.