DP/thunderbolt not working - firmware issue

[tmara]

The displayport and thunderbolt functionality on the USB-C ports of my Elitebook 840 G7 no longer work.
I discovered the issue after updating to the most recent bios (01.14.00), which includes a firmware update for the USB-C controller firmware.
However, the updated firmware fails to install (reproduced on second attempt below).

Attempting to roll back to a previous version (1.13 o before) gives a different error, which prevents a rollback of the USB-C controller firmware.

In either case, the bios install completes, and the computer functions normally (but without proper USB-C support).

Any advise on how to resolve the issue?

[tmara]

The error messages read:
> Update of the Intel Management Engine Firmware failed, because the target Intel Management Engine firmware update was found to be invalid.
> Timeout waiting for FW

I have also observed the following errors:
> Controller 15EB is not functional, TX ring full
> NVM write to address 0 failed with status=8
> NVM write to address 0 failed with status=2

But googling for these gives me no results