Mixcraft 9 Issue - no sound on export

If I put together a progression in Scaler 2, and then drag it into
Mixcraft 9…I hear no sound when I export to mp3 etc. But, if I change the tracks’ instrument to something else (like the M80 or Messiah) it records
to mp3 etc.
I recently bought an Alesis Keytar and a Alesis Q88, and thought it had to do
with that. But I have an akai keyboard midi and same thing. I did check
mixcraft preferences etc. I use other daw’s, but my son likes mixcraft.
Hoping to figure this out, if anyone had a similar problem.