audio waveform zoom bug?

Nuendo 7.1.20 on Mac OS X 10.9.5, 2009 Mac Pro. Having an issue where certain projects open with the waveform heights zoomed 100%. Sometimes this happens when I import an audio file, sometimes it happens when I copy a session from another machine. I can “fix” it by pulling the waveform slider all the way down, then at least I can work with the audio that way - otherwise it’s useless because I can’t see the peaks/transients. But pulling the slider part way down has no effect, it has to be pulled down to zero.

I saw another thread that suggested deleting the “.peak” images, but I have not tried that (I don’t know whether it’s safe to delete them or not).

Is this a known bug or something about my system?