grub2 - Ubuntu-MATE 18.04 LTS GRUB prompt on boot

Background:

I have been running Ubuntu MATE for a little over a year. I originally installed 16.04 LTS and then this year upgraded to 18.04 LTS, without any problems. Everything was great.

Issue:

I decided to upgrade the HDD in my Lenovo V570 to an SSD. Every time I boot my computer, I go to GRUB prompt. Even when I manually chose to boot from my SSD. I found this post - except in my case, I did not see the grub rescue prompt, but grub prompt instead.

So now, I always have to run the following commands on GRUB prompt, every single time I boot my computer, but at least I am making some progress! I followed this post explaining why and how to delete the MBR.)

grub> root=(hd0,gpt2)
grub> configfile /boot/grub/grub.cf

After booting into my system, I did this, but the issue persists:

$ sudo grub-install /dev/sda
Installing for x86_64-efi platform.
Installation finished. No error reported.
$ sudo update-grub
Generating grub configuration file ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found linux image: /boot/vmlinuz-4.15.0-23-generic
Found initrd image: /boot/initrd.img-4.15.0-23-generic
Found linux image: /boot/vmlinuz-4.15.0-20-generic
Found initrd image: /boot/initrd.img-4.15.0-20-generic
done

Pingback: post in the Ubuntu-MATE official community

I still do not know the root cause, but an accidental GRUB2 upgrade with default /etc/default/grub file, fixed this issue after a reboot. [Details]

Here is the script I used to update/upgrade packages on my computer, which FIXED all problem for me.

#!/bin/bash
apt-get -y update
apt -y upgrade
apt -y dist-upgrade
apt  -y clean
apt -y purge -y $(dpkg -l | awk '/^rc/ { print $2 }')
apt -y dist-upgrade --auto-remove --purge
apt -y autoremove
apt autoclean

Note, that this script simply updates, and does not actually fix the specific problem I was experiencing. Coincidentally, there was an update for GRUB2 and I had an opportunity to reset my grub file with default in the following prompt.

A new version of configuration file /etc/default/grub is available, but the version installed currently has been locally modified.
      │ What do you want to do about modified configuration file grub?                                  │
      │                                                                                                 │
      │                   install the package maintainer's version                                      │
      │                   keep the local version currently installed                                    │
      │                   show the differences between the versions                                     │
      │                   show a side-by-side difference between the versions                           │
      │                   show a 3-way difference between available versions                            │
      │                   do a 3-way merge between available versions (experimental)                    │
      │                   start a new shell to examine the situation                                    │

I chose option #1.