acrobat combine thumbnail quality low bit

When using Acrobat combine, user see what appears to be LOW BIT quality thumbnail images, as if they are like 4bit rate. Is there some cache I can clear out? I have restarted, and full revo uninstalled, reinstalled Acrobat, latest version whatever that is.

Searched and searched and can't find any hits on this situation. I'm sure its something small and simple.
The images work and look fine after comgine and open and look fine in windows photo viewer, its jsut inside acrobat combine thumbnails. 
Graphics drivers are up to date, the rest of photos all look fine across 3 monitors, these thumbnails all look the same across 3 monitors.

Ideas?