the issue could be linked to other processes that are running at the same time. When more applications are opened, AE seems to have trouble rendering transparency changes for RAM previews. Interesting…
The problem is not quite solved yet, but my conclusion for now would be: give AE as much room to breath as possible.
And yes, working with compressed video is never a good idea.
Thanks for your help and insights, Dave!
Stef Prein
director / motion designer at StudioFets.
Utrecht, The Netherlands
http://www.studiofets.com