For modern science not everything needs to be caused. The ontological causality is a dogma already disproved by science, which only uses the methodological causality.
So far science knows the following uncaused and spontaneous events: radioactive decay, Casimir effect, quantum entanglement, quantum tunneling, the quantum vacuum fluctuations, Hawking radiation, virtual particles.
Proof in science does not require causation, only requires experimentation. The radioactive decay for example, we abandoned causality for it, but it is proven, even without a cause. And the absence of cause is the explanation most accepted today. We have no reason to assume the ontological and absolute causality, without having how to prove this dogma, and I don't think that one day we will be able to prove that causality is always a necessity.
It may seem counterintuitive to say that causality is not an absolute truth, but in reality it only exists in the macro world. When we go to the subatomic world, many of our intuitions are not worth anything.
Those who say that absolutely everything has a cause with no exception is in fact defending a dogma impossible to prove, and science can't adopt dogmas as truths.