I can't duplicate that one. Perhaps you could tell us more information on how to duplicate it:
For example:
1. Boot RealBand
2. Select style _JAZFRED
3. PRess BB button to generate RealTracks
4. Highlight an area around bar 3 to 4
5. Select Generate button and "Generate BB - selected Region -selected tracks"

When I do that. all is well, and there is no blank region past bars 3-4.

You might try [menu] Make all BB "blue" tracks regular tracks - as maybe the issue is related to you working on the BB tracks.
Have Fun!
Peter Gannon
PG Music Inc.