That was when I scripted away a test that ran hundreds of times a day on a lower environment, attempting repro. As they say, at scale, even insignificant issues become significant. I don't remember clearly, I think it was a 5-10% chance that the issue triggered.
At least confirming the fix, which we did eventually receive, was mostly a breeze. Had to provide an inordinate amount of captures, logs, and data to get there though. Was quite the grueling few weeks, especially all the office politics laden calls.
With all the enterprise solutions being distributed, loosely coupled, self-healing, redundant, and fault-tolerant, issues like this essentially just slot in perfectly. Compound this with man-hours (especially expert ones) being a lot harder to justify for any one particular bump in tail latency, and the equation is just really not there for all this.
What gets us specifically to look into things is either the issue being operationally gnarly (e.g. frequent, impacting, or both), or management being swayed enough by principled thinking (or at least pretending to be). I'd imagine it's the same elsewhere. The latter would mostly happen if fixing a given thing becomes an office political concern, or a corporate reputation one. You might wonder if those individual issues ever snowballed into a big one, but turns out human nature takes care of that just "sufficiently enough" before it would manifest "too severely". [0]
Otherwise, you're looking at fixing / RCA'ing / working around someone else's product defect on their behalf, and giving your engineers a "fun challenge". Fun doesn't pay the bills, and we rarely saw much in return from the vendor in exchange for our research. I'd love to entertain the idea that maybe behind closed doors the negotiations went a little better because of these, but for various reasons, I really doubt so in hindsight.
[0] as delightfully subjective as those get of course
Amazon is mature enough for processes to reflect this, so my guess for why something like this could slip through is either too many new feature requests or many more critical issues to resolve.
If it's anything like how Azure handles this kind of issue, it's likely "lots of people have experienced it, a restart fixes it so no one cares that much, few have any idea how to figure out a root cause on their own, and the process to find a root cause with the vendor is so painful that no one ever sees it through"