I had been having issues with the composition window not updating when I moved my playhead. Anywhere in the timeline I'd move the playhead, the frame would not update. I'd have to wait a minute or so before the blue render progress bar in the lower right would even appear. Once it finally did the comp would resume normal behavior and quickly render whatever frame I was trying to view. The problem would keep recurring as I worked.
After two frustrating calls and screenshare sessions with adobe tech support insisting this condition is "normal behavior" I found the solution. The posterize time effect was causing the odd comp window behavior. The "stuck" state of the comp window would even persist into precomps without the effect.
Hopefully this will save someone some annoyance.