I had a brand new virgin SSD to use. Was not recognized. Attached the drive to my Winders 10 PC, formatted the drive to NTFS and ran a drive check. No problems. So I reformatted the drive to XFAT, saved a short .txt test file, all good. Reinstalled drive in Model 3, the drive was immediately recognized, formatted, and Sentry mode works well now.
Maybe the system can't recognize a nekkid drive...