Section of program will not export audio

See image below. This is a meditation. The vocal audio is the top (blue) portion, the music is the bottom (green) portion.

You can clearly see there is music during a gap where there is no vocal audio. This is intentional.

The music during this section will not export.

The piece exports perfectly - but that vocal gap where there is only music has nothing.

Please advise and thanks.

JF