Run sudo dpkg-reconfigure grub-pc and make sure it is correctly configured to install grub to your boot drive. If it is not, that would tend to lead to some of the errors you mentioned after grub is updated.
Run sudo dpkg-reconfigure grub-pc and make sure it is correctly configured to install grub to your boot drive. If it is not, that would tend to lead to some of the errors you mentioned after grub is updated.