MyCloud Mirror 6Tb (RAID)

Sorry but newbie here.
I have a 6 TB RAID configured device about a year old.
All has been set up ok but recently I had “Low Temperature " warning every few seconds (it lied, everything was warm!)
Rebooted and one RAID volume rebuilt - albeit slowly!
Today I have the same Low Temperature” Notification again and also:
" Volume Degraded
Volume 1 degraded. Please check status of drive by running Disk Test in Settings >> Utilities.
Thursday, 2018 November 22, 8:28:46 "

I ran the Disk Test as suggested and after 2 hours it hadn’t finished, so I cancelled it. How quick is quick?

Both Disks are reported HEALTHY.

So, what now please

Thanks Bob

Check if there is a new firmware available for your device. If no fw availabe then try to factory reset. If that does not work. Live with it or replace a new one if the device still under warranty.