i just recently started getting random 'silences' of drum sounds that i step entered in sonar professional.  a kick, tom, or cymbal (addictive drums) will be silent, but when i play the phrase back, i'll hear it, then another sound will be silent and i'll get the same result when i play back.
it doesn't effect the exporting of the track, but it is annoying.
 
Pat
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Sounds like a buffer issue. Possibly dropping notes . Try changing your buffer size to 500

Hi, and welcome to this forum.
Try increasing the "Prepare using ... ms buffer" to 500 in Preferences, MIDI, Playback and Recording.
Hope it helps.
All the best.

Hi Patricio
Exactly the same thing happening here with vst instruments. Random notes drop out but fine on export. Will try the suggestions above too to see if it helps.