One dodgy lamp: Differential is triggered and several separate circuit breakers become differential-triggering. How is that even possible?
Perhaps a neutral-to-ground short in the lamp, which is not disconnected by opening its breaker, is creating a current path impacting other circuits.  I can't say exactly how as I don't know exactly how the multiple RCDs on a panel interact with one another through their common ground and neutral bus.  But it's the only possible explanation.  I'm guessing you are in a home with European-style RCD groups controlling everything in the house, is that right?