In my time writing databases, I found that not only the mount-flags could result in data-loss despite fsync, given you use fsync as it is supposed to be used [0], but even enterprise-grade hardware would at times (at that scale [1]) drop and/or corrupt a few bits here and there.
That reminds me of the case where AWS famously revealed that a single NIC in their ginaromous S3 fleet flipped a single bit once in a while and that caused an outage because their gossip-daemon responsible for fleet health-checks failed spectacularly [2].
Bryan Cantrill's talk on the realted topic of hardware/firmware bugs is pretty good [3].