I don't use Adobe in any fashion but your inquiry made me curious.
I found this in case you may have missed an aspect of what Adobe recommends for file exporting/saving and the formats supported.

https://helpx.adobe.com/audition/using/saving-exporting-files1.html

Also....is it possible the file names you are saving are too long?
Maybe Adobe defaults to that .17 extension for that reason?

I'm just shooting from the hip so don't know if this is any help.
But, you got bumpeth.

Carry on.....