X1C - Unexpected loss of Clip audio

This is a wierd behavior I've never experienced in Sonar before X1C.  During playback of recordings I made yesterdy on a Vocal track, sometimes the first clip from wherever the "now position" didn't sound at all.  One time, part of the clip played, and then went silent half way through.  This behaviour was intermmitent.  I couldn't replicate it.  But it seemed to occur with only the 1st clip from the "now" position.  It happened about 4 times yesterday. 
 
This didn't happen during the actual recording session - when I usually had the track armed - or if it did, I didn't notice it.  It only happened after the recording session when I mixing and editing.
 
I'm using Sonar X1C 64bit with Windows7.
 
Anybody else getting this?