TW12: Clip won't play after Warp Time adjustments...

[Ally007]

Hi all. Today, I did some warp-time adjustments on an audio clip, as I've done countless times before. However, today, I find that the clip then won't play back; it's as if it's muted. Also, if I uncheck "show clip effects", the clip goes blank (the graphical sound wave disappears completely). I tried relaunching TW12, but there was no change. Can anyone suggest a possible cause? Thank you.

[dysjoint]

Is 'use proxy file' checked? (in the clip properties)

[Ally007]

Is 'use proxy file' checked? (in the clip properties)

Thanks, but I cannot find a 'use proxy file' option anywhere. It's not in the left panel or the bottom middle panel (clip details and/or loop properties tabs). I did select the clip, before looking.
Update:
I must have done something wrong. I just noticed the clip now had 4 waveforms instead of two (stereo). I hit 'Undo' till it reverted back to the two (stereo) waveform state and the problem disappeared. I'm not sure what I did to end up with 4 waveforms in one clip!