Since I have upgraded from 6.8.3 there is weird bug.
After some time disks are shown to be in stand by (gray status).
But problem is that I can clearly hear that some disks are still spinning.
I haven't had this issue with previous version of Unraid.
When this happens, I have found workaround to spin them down manually:
first I need to spin them up (I guess to GUI gets update that they are actually spining)
then I can click on spin down and all of them will spin down
If I skip first step, nothing will happen.
So issue arises only when they "spin down" after idling for some time.