Installer mounts USB EFI partition at /target/boot/efi causing grub-install to fail

I had the Kubuntu 20.10 installer on a USB stick, and was attempting to install Kubuntu to the SSD in my Dell Inspirion 7370 laptop. During the install, the USB stick was assigned /dev/sda, and the SSD /dev/sdb.

I observed the installer incorrectly mounts the USB stick EFI partition at /target/boot/efi during install causing grub-install to fail. I could consistently trigger the issue with the following sequence:

1. Start Kubuntu 20.10 install
2. Select standard install, download updates during install, and enable secure boot
3. Choose automatic full disk partitioning, with LVM and encryption enabled
4. Install fails with 'grub-install /dev/sdb failed', which is a fatal error

The following workaround was required:

1. Immediately after choosing automatic full disk partitioning and confirming, move to a terminal
2. sudo umount /target/boot/efi
3. sudo mount /dev/sdb1 /target/boot/efi
4. If this is done quickly enough before the grub-install step, the install now succeeds

The workaround has the following issue:

1. The USB sticks EFI partition UUID is incorrectly written to the newly installed systems fstab for the mount point /boot/efi
2. The first boot post install fails, and the system drops to an emergency shell
3. Correcting the UUID in the fstab for /boot/efi and rebooting resolves this problem.

I assume this is due to my laptop assigning the SSD /dev/sdb, and the USB /dev/sda, however all other /target mount points were correct - only the EFI system partition was incorrect.