I had this happen the other day.

MIDIs would play, notes that were entered would play. But when adding the notes you would not hear the new note as it was added.

I exited RB and restarted it. After that I could hear the entered notes again.

There were no setting changes or anything else out of the ordinary, it just stopped playing the notes as they were added until I restarted the program. Note I did not restart the computer, just the RealBand program.

So if the suggested setting didn't help and you have this happen again try restarting the program.

Burt