linmob:
I checked for differences in relevant firmware , and this might suggest a solution:
$ sudo cat /sys/kernel/debug/tps6598x/0-003f/customer_use
returns 0x4c35445000000101 for my older, working Librem 5, and 0x4c35445000000200 for my newer Librem 5, that does not work with the Dual Up.
That is the firmware for the USB PD controller. I made a post listing upgradeable firmware, but I can no longer edit it due to its age; I would add the touchscreen firmware to the list if I could.
As far as I know, including those mentioned, there are a total of 6 (2 are combined):
DAS U-Boot
TTXS (Smartcard Reader)
USB PD Controller
Firmware Jail (also includes Redpine RS9116 firmware)
BM818-x1
The first four on this list can be performed sequentially directly during and after reflashing the Librem 5. The last two are performed on the Librem 5 itself.