I think this may be a operating system problem as someone else pointed out perhaps the drives are in sleep and nas is not giving enough time to awake
I just brought a new t9 3 weeks ago and 5 new hard drives all was fine until this week all I keep getting is messages it’s degraded hhd 1,3,5
And all happened in the morning after not using all night it seems shutting down the nas and pull the drive then reinsert and reboot everything back all drives seen and all data is back also using TOS 5.1.145 or is it possible all 3 drives have failed within 3 weeks all at the same time