The loss of project audio (numbered audio tracks and soundtrack) after the addition of narration from the program's Narration Tool is a known issue.
The fix of Llamadude99 is described in the following blog post.
It has worked for many already, please let us know if it works for you.
Thank you for sending me this. Different things seem to work with different setups. I have used these work-arounds, and at least one of them works, so the sound is back
Adobe should update program with solutions!
Many thanks for the follow up with the great news that your project sound is back.
If your schedule permits, would it be possible for you to describe which solution (or variation thereof) in the post 1 link worked for you?
This is a particular disturbing audio/Narration Tool narration problem that does not affect all, but the numbers of reports of its
happening seem to be increasing. If you have not already, please update from Premiere Elements 12 to 12.1. I do not believe that
to be the answer to this particular issue but it will help you with any Expert workspace Text Style issues at least.
Your follow up report is a contribution to addressing this audio/Narration Tool narration problem.
This problem seems to be corrected by different, but similar actions. In my case, I too the microphone off-line and then stopped (cancelled) the mute box in the narrative recording, and that appears to have resolved the problem, though I had to do it again after recording more narrative.
A permanent fix would be preferable. I have upgraded to Premier 12.1 and that does not solve teh problem