While it could certainly be a card-reader problem, data corruption of any kind can be any of the following:
1) the card
2) the cable (if used)
3) the card reader (if used)
4) the computer RAM,
5) thecomputer hard drive (or SSD)
A failure of any one of the above will result in corrupted images when viewed. Since it seems to be RAW file related, as they are signifantly larger than JPGs, it's likely anything but the card reader or cable.
The only way to 'beat it' is eliminate each of the possibilities, starting with the easiest/cheapest fix.
1) Use the cable. If that solves the problem, replace the card reader.
2) Use a different card. If that solves it, toss the old card.
3) If multiple sticks of internal computer RAM, swap them. If that fixes it, or, the problem 'moves' to other images, replace the RAM. It could be only 1 of 2 sticks bad, though, so use only 1 of the old sticks for a while to see if the problem recurs.
4) If you have multiple hard drives in your computer, or an external one, use that to store the photos for a while. If the problems go away, it's the drive. Note that hard drive failures typically start slowly and increase gradually. On occassion, though, your computer won't boot and it's all over. If you are down to thinking it's the hard drive, it's time to get a good backup...NOW!
For what it's worth, I had a similar problem with corrupted photos. Both RAW and JPGs were affected. But as the problems were after having loaded and initially viewed them on my HD, I knew it was a computer problem. It dogged me for a couple of weeks. I even played swap the memory sticks, pull one out and run on one only, swap the one for the other (running on one), and it STILL kept happening. I finally gave up and replaced both sticks of RAM. That solved the problem. So much for lifetime warranty from Hong Kong. A very well regarded brand of RAM, no less. My SSD drive was the next one on the list, it the new RAM didn't solve it.
