There is a "main" sequence consisting of 14 nested sequences. Each of the 14 nested sequences are a "target" sequence (Adobe help terminology) made by nesting a multi-camera sequence and going through the cut process.
When these 14 targets are made, the audio works.
Now, back into the main sequence, two of the 14 have no audio. Render Work Area and Render Audio do not help.
I went to the target sequence and its audio was now gone. So I tediously rebuilt the sequence and the target audio was now present. Went to the Main sequence and the audio was present.
But then I performed a Render Audio on the main, and immediately upon completion, the audio was gone!!!! Just for sequences 1 and 2 (the audio is still functional with the other 12 sequences).
I repeated the entire tedious experiment, and it happened a second time!!!
I compared the Sequence Settings of the working sequences and the non-working sequences, they appear to be identical.