That is a crazy problem. Have you tried to power off (POWER OFF) and power back on, see what happens? I say power off to kill power to the hard drives, not that that should make a difference but you have a strange problem.
If that fails to work, hopefully someone can offer assistance.
1) Do you know if all your data is still accessible? And do you have a backup? Hopefully you will not need to use it.
2) I would file a Bug Report (ensure to include the log data or you will be doing it later).
3) Hopefully someone will be able to give you some good advice.
I don't know if SCALE is to blame here but I will not migrate to SCALE for many months, MANY. So many issues with the pools, scarry.
I wish you the best of luck.
EDIT: Did you by chance have a "Spare" drive in the system?