exfat drive, folders visible, files not visible

Macbook Pro late 2007

I replaced my optical drive with a 500gb exFAT formatted hard drive (formatted using Windows). I am running El Capitan, boot camp, and Windows 10 installation on the main drive. The exFAT drive is showing in both Mac OS and Windows. Windows has no problem and can see all files, folders, etc. However, Mac OS will only display the folders on the drive. When you open a folder, no files appear. I've tried running First Aid, but receive an error: Unable to unmount volume for repair.

reset SMC and PRAM with no relief

Is it possible that allocation unit size is the problem here?

'131072 bytes in each allocation unit'

any workaround or fix without reformatting?