If it's only hit once by a random person, memory starts being more likely.
(Unless that LOC is scanning memory or smth)
Also, in an unsafe language all bets are off. A memory clobber, UAF or race condition can generate quite strange and ephemeral crashes. Even if the majority of time it generates the “same” failure mode, it can still sporadically generate a rare execution trace. It’s best to stop thinking of these as deterministic processes and more as a distribution of possible outcomes.
This is a bit vague to really reply to very specifically, but yes, this is hard. Which is why quite some people work in this area. It's rather valuable to do so at Firefox-scale.
Even if the majority of time it generates the “same” failure mode, it can still sporadically generate a rare execution trace.
This doesn't matter that much because the "same" failure mode already allows you to see the bug and fix it.