This question has bothered me for some time but it's become more critical with increased audio render times in PP CC. Why is it that I can end an edit session with all the audio waveforms visible and then open the project the next day with nothing changed and have some of the audio waveforms in the sequence blank? I know I can bring them back by clicking on "render audio" but that can take quite a bit of time and space. Today, for instance, render audio took between 5 and 10 minutes and created eighteen 2 GB files in the Video Cache folder. (This test was with PP CS6.) This is the same number and total size render files that were created yesterday when I did a render audio. So my questions are: (1) what can I do to keep the waveform from going away? and (2) is there some other way to bring it back? This general problem happened with CS5 but the render time wasn't as great then as the render files were smaller.
My guess would be a system issue of some type. This is certainly not normal behavior. Possibly a redraw issue with your graphics card or driver.