I don't know if this is a bug but I wasn't sure where else to post it.
I have two spindown problems in RC2:
I've set default spindown to 15 minutes to help with testing.
(1) The USB disk in Unassigned devices
Unraid tries to spin it down (good!) but doesn't actually do it. That may be a problem with the drive's USB interface so I've cron'd a user script to spin it down with hdparm -y /dev/sdb (which works.) It looks like unRAID never detects that it
Specifically it's the smartctl calls in telegraf (part of GUS.) Alternatively you can comment out the [[inputs.smart]] block in Grafana-Unraid-Stack/telegraf/telegraf.conf to disable them.
Seems for whatever reason (new kernel, new smartctl) these calls are recorded as disk activity which causes the disks to fail unraid's "If inactive for X minutes, spindown" test.