I've seen this in the past once or twice, and have never figured out the cause.
I found it better to, as you mentioned;
Copy the desired section to another Track and then delete the offending Track, use Save As and just keep working.

I assume it's a file corruption as I have never found another audio Event or such that would logically cause it. That's why Save As is an important step.
Then once I know I'm good I'll delete the old one.


I do not work here, but the benefits are still awesome
Make your sound your own!