https://forum.manjaro.org/index.php?topic=10354.15

This will fix it:
/etc/default/grub

# If you want to enable the save default function, uncomment the following
# line, and set GRUB_DEFAULT to saved.
#GRUB_SAVEDEFAULT=true

Comment out GRUB_SAVEDEFAULT=true like shown above.



!!!
And remember to do a

sudo update-grub