Ducking issue in 4.6.3

I have assembled a program with photos and a section of video. I arranged ducking to lower the musical soundtrack when the video segment with talking comes in the timeline. All works as it should. The program plays with the ducking as arranged. The problem is when I tried to save the program for YouTube or as a full .mov file, the soundtrack is not lowered for the video segment and the video segment has no audio playing. Any thoughts on what could be the issue.