Update: Just looked at the cabling and connectors yesterday, there is no obvious reason like loose plugs or broken wires.
As Jens mentioned, there is a mess of cables there, so in case you want to play around, do mark them properly! I used tape and noted the function on it.
The low beam input from the source was already marked 'low beam' at my bike, so it was relatively easy to identify cables and connectors.
The LED driver at the bottom is the one for low beam, the upper one is for high beam.
(Update: Not correct, the two LED drivers are dedicated to one lamp, i.e. lower one for the left, upper one for the right lamp.)
Connectors for both are the same, so I did not extract the LED drivers (that appears to take a lot of disassembling work), but only switched the connectors.
That works as Jens indicated: High beam driver is now working the low beam, nice workaround!
When I then switch to low beam (i.e. the low beam driver is then trying to power the high beam lamps) only the right lamp is lighting up for a second, left side remains dark and after some time the fault message comes up. I regards this as a clear sign that the LED driver has died.