First of all it would be very interesting which firmware versions are installed on your Librem5 
to check whether that has been the cause of our different findings.
About updating: First of all: if you update you can break things. If you do not know how to repair them you might need help to do so and you will not be able to blame support for having you told to update.
You can find information about the firmwares on the wiki page about troubleshooting docked mode. There is a reference to the repo of the TPS65982 firmware and information about the Display Port firmware.