There are many interpretations of QM, and those different interpretations may answer this question differently.
In pilot wave theory, some apparently-random event was in fact not random but determined by some process (which I don't know the details of) which decided that would happen.
In many worlds, some apparently-random event happened because it was guranteed to happen (not in all worlds, but in some world), by having some amplitude in configuration space that corresponds to that event, without being destructively interefered with.
In copenhagen, I think it's generally considered that yes, there's no sufficient reason - it's truly random.