Frequent Degraded needs rebuild every 2-3 days

My 4Tb My Cloud Mirror has a drive that gets degraded ever 2-3 days and I need to reboot and then it rebuilds and then is fine.

For another 2-3 days.

Why does it do this? I have around 250Gb left on the machine - it is fairly full but it should not have to be rebuilt twice a week…

Anybody else experience this?

I’d recommend scanning that hard drive for errors, and to replace it if it fails the diagnostic test.