Sorry for this inconvenience.
How exactly that you are importing the images to Lightroom, please share the complete workflow.
Also you can try this.
Click Lightroom -> Preferences ->Performance
Uncheck Use Graphic Processor
Close Lightroom and reopen
Now import and try.
This sort of corruption is normally always hardware related. if you are seeing it across multiple hardware, look for something common between all your gear.
e.g. Are you using the same card reader and cable on both Macbooks?
Thanks a lot for your answers. Its looks like the issue was hardware related and Phil323uk was correct.
My Lexar Workflow CFR1 card reader didn't like ElCapitan... I swapped out the card reader and all is fine again. Will try to find a firmware upgrade for the card reader (when such a thing is existing) or just only use the other readers I have ... :-).