The dealer probably did spot the fault, however, as it is not current they will have cleared it as the system is working.
Take it back to them and say the error came back, they should be able to see the stored fault again. I think the headlight module is intermittently faulty, it will need a new module to fully go away.
I have a similar issue with my distronic module. Intermittent fault which last until I turn off the car and restart. The fault in STAR diagnostic points to the module. I will either live with it or replace the module.