I've imported DNGs from various cameras over the years yet LrCC won't display Leica 240 DNG thumbnails as images in the Import dialogue. It'll only display them as generic DNG logos.
I only ever shoot RAW and never shot RAW+jpeg yet I've experienced this issue with importing rom any other camera or raw file.
Any idea anyone? I'm sure it's something simple.
Please try restoring Lightroom preferences back to default.
Also, if you check the same image in Bridge do you see the DNG Log or Image.
Let us know if that helps.