You say "in Photoshop CC" but the screenshot is of Windows Explorer file selection so what isn't working is some sort of Windows codec to render DNGs. You'd see the same lack of thumbnails if you opened Windows Explorer on a folder of PSD or raw files.
Did you have a Microsoft Raw or DNG Codec installed? There used to be one, but I don't know if there is currently.
I use the Fast Picture Viewer Codec Pack on my computer to see various image thumbnails:
Thank you. Meanwhile, I downloaded Windows 10 and now I see DSC, raw thumbnails but NOT PSD thumbnails.
I wish Adobe would fix this as its annoying having to open Bridge just to quickly have an overview of what is in the PSD file. Thumbnial and preview pane in windows should just be supported with each update they do. As these other external plugins become redundant with every other Photoshop update.
Anyways doubt this would be read by any Dev or Adobe member... but we'll take that $50 each month thanks rant