Welcome to the forum.
There have been a few instances, where it seemed that the Narration Track has become "locked," but have not seen a direct "fix."
Here is a workaround. Download and install the free audio-editing program, Audacity. The trick will be to get a video, if you need that to time and prompt the narration into Audacity. PrE's playback will stop, when that program looses focus. I'd do an Export/Share for a "reference file," and use a player like VLC, or WMP to view the file, listening with headphones, and then record into Audacity, using the meters as my guide.
I use Adobe Audition, that will allow me to Import Video and use it as a reference, but that is a rather expensive (though great) program. Audacity is free.
I'd love to know what causes the Narration Track to go wonky, but have not see the answer to that. There is a fairly recent thread on this forum with the same problem. You might also want to Search this forum for "Narration Track," and then can filter on People, using either me, Bill Hunt, or Steve Grisetti, to limit some of the hits. Check them out, and you will quickly find the longish thread that I recall.