ARW Files from Sony A7RII
MacBook Pro with Retina display, OS X Yosemite (10.10.5)
Most likely is because you are way behind in OS updates - you state you have OS X 10.10 5 which is six updates behind - the current software is OS X 10.11.6 - update to the current version of El Captain and you should be fine
LN
Select one of the black thumbnails and try, if reprocessing the RAW will help. The last RAW support update you installed may have changed the RAW processing for your camera.
To reprocess the RAW fileopen the image in Edit mode and use the command "Image > Reprocess RAW". Does it bring the correct thumbnail back?
ARW Files from Sony A7RII