This issue can be encountered because Sony supplies their RAW files with reduced-size JPEG previews. This issue was fixed for the newer Sony cameras but persists in some older models. There are two ways this issue can be fixed.
Solution 1 - Shoot RAW + JPEG
If you shoot in RAW + JPEG using a Sony camera, you can go to Aftershoot’s settings and instruct it to read the accompanying JPEGs for your RAW images.
This will make Aftershoot render the accompanying JPEG files instead of relying on the lower-resolution embedded thumbnails.
Solution 2 - Use Lightroom to convert ARW to DNG
Alternatively, you can convert your ARW files to DNGs in Lightroom. Afterward, simply import the DNGs into Aftershoot. This way it will cull and display the full-resolution thumbnails for your images.
One thing to keep in mind is that the DNGs need to include full-sized JPEG previews.