UC20 boot error "Failed to make path absolute" on Fitlet2 device

Trying to build a custom image for the Compulab Fitlet2 (just a extended pc-amd64-gadget) and kept getting this error. Using the original ubuntu-core-20-amd64.img.xz from https://cdimage.ubuntu.com/ubuntu-core/20/stable/current/ results in the same error. The device is booting of USB key.

Already have a working Core16 image, device can run regular Ubuntu 20.04 from USB. Image works on laptop and QEMU, just not on this device.

Error reads:
`the-tool[237]: error: Failed to make path /dev/disk/by-partuuid/...: No such file or directory`

Partition UUID matches the ubuntu-seed partition of the official image, on the custom image it points to the ubuntu-boot partition. Have tried different USB keys, but all of them report the same error.

Device specs:
- Intel Atom X7-E3950
- 4GB Memory

Just to be sure I tried booting using UEFI and legacy mode, with and without secure boot enabled (not configured), all result in the same error.

USB is "hp v195b" which is logged at 2.7 in the screenshot, after the error has occurred. However other tests show that the error occurs after the message related to the USB key.