Automatic upgrade from Ubuntu 16.04 o 20.04

[rpstew]

I have hardware with a single SSD imaged with six partitions:

1. EFI
2. /boot
3. swap
4. recovery (Ubuntu Server 16.04)
5. / (Ubuntu Desktop 16.04)
6. /home

I also have another image that is very similar, but with 20.04:

1. EFI
2. /boot
3. swap
4. recovery (Ubuntu Server 20.04)
5. / (Ubuntu Desktop 20.04)
6. /home

I have been tasked with coming up with an automatic upgrade process from Ubuntu 16.04 to 20.04. I have a process in place that overwrites the Ubuntu Desktop 16.04 partition (partition 5) with the Ubuntu Desktop 20.04 partition. This is done from the recovery partition using "partimage -b restore". Only the 5th partition is overwritten. After that process the hardware fails to boot with the following error:



I ran the boot-info tool and got the following: https://paste.ubuntu.com/p/gMHZ8Nnm7H/
I notice several issues in those logs:

• line 67: Normal Mode shows 16.04, but should show 20.04
• line 109: grub-pc added (not sure if this is an actual issue or not)
• line 117: fstab-has-bad-efi
• line 125: fstab-has-bad-boot
• line 165: UUID changed of partition 5 (this is expected)

I'm not sure how to address these issue. Please advise.