From the debug logs, the mount ordering looks correct so I can't explain why mounting /boot/grub2/x86_64-efi fails. For the record, the command is: /usr/bin/mount /dev/disk/by-uuid/d4da036b-b69a-4717-9d82-935e0d764cd8 /boot/grub2/x86_64-efi -t btrfs -o subvol=/@/boot/grub2/x86_64-efi and fails with return code "32", which basically means that the mount syscall fails somehow I think. So something went wrong in the kernel I would say.