Re: GRUB Problems "error: unknown filesystem"
You have a complicated setup on a new filing system where RAID 5 is not fully supported by BTRFS out the box yet so you are using software raid.
You may want to ask in #btrfs on freenode and see if anybody has the same setup as you, if no one here can help you.
You say it's working in Mint. I would compare and contrast the differences between the setups.
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