Rescue partition in Yocto image - yocto

Question

I need to create an image using Yocto that includes a rescue partition. That is, another root partition which is selectable in grub menu.
I am currently creating an image which I dd to our target Intel board's internal SSD chip after booting from USB. This is working, but I now need to duplicate the current root partition as a "rescue" partition for in case something ever goes wrong with the root partition.
So currently I have a working wks (kickstart) file with 5 partitions defined as:
part /boot --source bootimg-efi --sourceparams="loader=grub-efi" --ondisk sda --label boot --active --align 1024
part / --source rootfs --ondisk sda --fstype=ext4 --label root --align 1024 --use-uuid --extra-space 1024
part /rescue --source rootfs --ondisk sda --fstype=ext4 --label rescue --align 1024 --use-uuid --extra-space 1024
part swap --ondisk sda --size 1024 --label swap --fstype=swap
part /home --ondisk sda --fstype=ext4 --label home --align 1024 --use-uuid --size=1024
bootloader --configfile="grub.cfg"
The grub configuration has two menu options and I am able to boot from the default first menu option.
menuentry 'boot'{
linux /bzImage root=/dev/sda2 3 console=ttyS2,115200n8 rootfstype=ext4
}
menuentry 'rescue'{
linux /bzImage root=/dev/sda3 3 console=ttyS2,115200n8 rootfstype=ext4
}
The grub configuration selects the second or the third partition as root. This works with the fixed order of partitions in the wks file.
My problem is that if I select the 'rescue' partition in grub, the system starts to boot but the Linux kernel fails to find a root partition. Here is the last kernel messages before the kernel panic:
:<snip>
:
ata1.00: ATA-8: 32GB NANDrive, D A431F4, max UDMA/133
ata1.00: 62533296 sectors, multi 0: LBA48
ata1.00: configured for UDMA/133
scsi 0:0:0:0: Direct-Access ATA 32GB NANDrive 31F4 PQ: 0 ANSI: 5
sd 0:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
sd 0:0:0:0: Attached scsi generic sg0 type 0
sda: sda1 sda2 sda3 sda4 < sda5 sda6 >
:
:<snip>
:
List of all partitions:
0100 16384 ram0
(driver?)
0101 16384 ram1
(driver?)
0102 16384 ram2
(driver?)
0103 16384 ram3
(driver?)
0800 31266648 sda
driver: sd
0801 24571 sda1 9f293dfb-01
0802 4151722 sda2 9f293dfb-02
0803 4151722 sda3 9f293dfb-03
0804 1 sda4
0805 1048576 sda5 9f293dfb-05
0806 1048576 sda6 9f293dfb-06
No filesystem could mount root, tried:
ext4
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,3)
:
:
I suspect Yocto does something when building the image which I just need to control but am unable to find the source of this problem.
Any help is appreciated