I can report the exact same issue with a fresh 16.04 install.
I did manual partitioning, left the requisite 1MB+1MB free for grub and it now boots to grub-rescue with a message about an unknown filesystem. I booted into rescue mode and ran grub-install /dev/sda which annoyingly installed on my usb install fob (that will teach me not to check device names).
I'm now running grub-install on the booted system and will see if it reboots.
I can report the exact same issue with a fresh 16.04 install.
I did manual partitioning, left the requisite 1MB+1MB free for grub and it now boots to grub-rescue with a message about an unknown filesystem. I booted into rescue mode and ran grub-install /dev/sda which annoyingly installed on my usb install fob (that will teach me not to check device names).
I'm now running grub-install on the booted system and will see if it reboots.
Nope. Still broken.