This problem has just cropped up. Working on two different projects, and some of the wav files in both projects do not show wav data, although the clip plays. Bouncing to clips rectifies the situation, but it's a big pain, and time suck. Wondering if this is a bug in the latest release.

Not really a solution, but instead of bouncing (which takes up disk space) you could recompute the picture. Just right click it to open clip properties.

You may also need to empty your picture cache folder. 

Thanks! Will try both suggestions. Never seen this happen in my over 20 years of using Cakewalk.