peter You can only generate the waveform from the longest track. So if you don't see the option on some tracks, they are shorter than another track in the song.
I've just been 'caught out' by this feature and it had me scratching my head as I was seeing inconsistent behaviour as I added a mono stem to a few of my existing multitrack songs.
I had always seen the generate waveform
option on all wave files in my multitrack songs, so I was scratching my head as to why it was disappearing from my existing tracks and only showing on the just added track, and only for 1-2 of the songs I was working on.
My first thought was that while I understand the logic behind the decision, it was still quite frustrating.
Then I found an upside! It had inadvertently alerted me to the fact that I had screwed up the track export from my DAW, resulting in a wave file of different length to my main backing/click/cues, and was also going to be out of time!