Errors during upgrade from 17.10 to 18.04 (shim-signed and grub-efi-amd64-signed)

After running sudo do-release-upgrade this morning to upgrade my system from Ubtunu 17.10 to 18.04 LTS, I encountered errors during the upgrade. The trace is too long to post in it's entirety, but here is the part that (to me) looks like the problem:

Rebuilding /usr/share/applications/bamf-2.index...
Errors were encountered while processing:
 shim-signed
 grub-efi-amd64-signed
Exception during pm.DoInstall():  E:Sub-process /usr/bin/dpkg returned an error code (1)

Could not install the upgrades 

The upgrade has aborted. Your system could be in an unusable state. A 
recovery will run now (dpkg --configure -a). 

Setting up shim-signed (1.34.9+13-0ubuntu2) ...
Installing for x86_64-efi platform.
Could not add entry to BootOrder: Interrupted system call
grub-install: error: efibootmgr failed to register the boot entry: No such device or address.
dpkg: error processing package shim-signed (--configure):
 installed shim-signed package post-installation script subprocess returned error exit status 1
Setting up grub-efi-amd64-signed (1.93+2.02-2ubuntu8) ...
Installing for x86_64-efi platform.
Could not add entry to BootOrder: Interrupted system call
grub-install: error: efibootmgr failed to register the boot entry: No such device or address.
dpkg: error processing package grub-efi-amd64-signed (--configure):
 installed grub-efi-amd64-signed package post-installation script     subprocess returned error exit status 1
Errors were encountered while processing:
 shim-signed
 grub-efi-amd64-signed

Upgrade complete

The upgrade has completed but there were errors during the upgrade process.

I've browsed the forums for solutions and can preemptively confirm that the entries in /etc/fstab are not commented out. cat /etc/fstab outputs the following:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda9 during installation
UUID=a2f91309-dc7e-4456-b3ef-89900b145365 /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sda2 during installation
UUID=90EA-4FB8  /boot/efi       vfat    umask=0077      0       1
# swap was on /dev/sda6 during installation
UUID=2f80d8f4-5609-45e1-854d-578ab25836c3 none            swap    sw              0       0

The system is a dual-booted with Windows 10. Through lsb_release -a I can confirm that my Ubuntu partition did update to 18.04 LTS, but these errors unnerve me and I don't want them causing problems in the long term. Thank you.

I had the exact same error. The solution I found in order to upgrade the remaining last 2 packages was:

sudo su -
cd /boot/efi/EFI
mv ubuntu ubuntu-old
apt install -f
mv ubuntu-old ubuntu
update-grub2
exit

I hope it helps.