I had this before with Camry and hit same issue with NX.
I had 9 folders on USB, each one containing whatever number of MP3 files.
I had NO ISSUE whatsoever playing any of them on my Highlander. Same USB. I had JBL head unit there.
Nx will show only TWO folders. That's it.

That brings me to a question:
1. Does an audio file have to be in a folder, to be read by NX headunit?
2. How do I make it play multiple folders? More than two, I mean. I can't move those folders content into one of the recognizable folders, as those are discourses in certain order and on certain topics. So it will all become a hodge podge if I were to move audio files into two folders only.

Thank you

 

I have several (12 or so) folders on mine. My NX plays them all just fine.

You might check the type of MP3 you have. Bit rate, etc. look for similarities in the ones that play and differences in the ones that won't.

 

They are all same, MP3 that played fine in Highlander. I simply took that USB out of Highlander when I sold it and plugged into NX when I bought it. USB is FAT32 formatted, I know that.