I reset my Tablo 4 tuner as the last drive failed and attached a WD Passport Air usb external drive that I previously was using with my MacBook Pro. The Tablo app states no hard drive found but when I go into recordings from the app on my Apple TV it shows the shows recorded that I set up to record but they fail to play stating “no hard dive found”. Are only the WD Elements and Seagate Expansion drives supported? https://www.tablotv.com/blog/how-much-tablo-dvr-recording-storage/
Format the drive on your computer to FAT32. Then reboot aka power cycle your Tablo.
If that doesn’t work, factory reset your Tablo.