Comment # 2 on bug 965503 from Roman Bysh

I found the following on the Archwiki:
Ref: https://wiki.archlinux.org/index.php/Btrfs#Partitioning

GRUB can boot Btrfs partitions however the module may be larger than other file
systems. And the core.img file made by grub-install may not fit in the first 63
sectors (31.5KiB) of the drive between the MBR and the first partition. 

I have read that users partitioning with fdisk and gdisk avoid this issue by
offsetting the first partition by roughly 1MiB or 2MiB.