How did my audio become unmapped? the fix was mapping but how did it happen in the first place?

Thank god for this post. 

Audition Audio Only Playing Through Left Side of Bose Headphones

I don't know what happend but any help would be appreciated so I don't do that again. First, my mixdown wouldn't export to premier correctly then I tried to close down audtion and when I reopened I could hear no audio and then I want to reopen another project and it came in only on the left side. 

I think someting got wonky with the dynamic link.