This looks like image corruption caused by failing hardware, and from your description it sounds like the corruption is happening when the image is transferred to the computer. If you connect the camera directly to the computer, it could a failing USB cable, or the cable is not properly seated in the camera, causing intermittent failure.
Using a card reader to transfer the photos to the computer is not only safer and less error prone, but also much faster.
And the image you see on the back of the camera is a jpg embedded in the raw file, and these jpgs are for some reason usually not corrupted, so viewing the files in programs that can't render the raw file itself, will not show the corruption.
I agree this is caused by a hardware malfunction somewhere.
I don't agree that card readers are always the solution, I have had card readers fail (especially if they are the cheap ones) and cause this, but I have never had this happen when I hook my camera up to the computer by the manufacturer-supplied USB cable. Some card readers will be more reliable and less error prone, but not all.
That would seem to be the obvious answer IF it was happening on import. But this is occurring after the files are already on the drive and look OK. I can watch the corruption happen! The image comes in OK then LR goes through the images and scrambles them. I'm using a Hoodman Steel UDMA reader BTW. I shot a couple of frames just to see if it would corrupt them too and they came in OK and stayed that way.
It still could be the card reader, 2 frames isn't much of a test. I'll shoot a bunch of test stuff and see what happens with them when I bring them into LR.
The image you see in the import dialog, and initially in Library before the raw file has been rendered, is the embedded jpg preview.
So when Lightroom "scrambles" them, it is actually changing from the embedded preview to the raw file.
Since you are using a card reader, the reader itself, or the cable/connections could be causing the corruption, or there could be a problem with the card itself.
I would first check the cable and the connections, and also try with a different card.
Also try connecting the camera directly, if that consistently works, there is likely to be a problem with the card reader or cable/connections.
Yup, thought of the JPG preview vs raw rendering after I posted my last. Could have been the USB connection to the reader itself, it's not hard wired. We'll see.
It was the CF card. Tried several other cards and they worked fine. The card is on it's way back to SanDisk for replacement. SanDisk customer service was great, told them the issue and they said send it back.