There are two issues
1) if the wave does not get drawn, but the audio is theree on playback, then empty Picture Cache folder
2) If the wave dissapears and there is no recording upon playback
a) You may have autopunch enabled in Record dialogue box, it will only record between thr punch in and out point. Therefore disable auto punch
b) You armed the track and hit play instead of record, or hit record record on another track where what you were recording wasn't routed too.