While I'm sorry you had bad experiences upgrading to iOS 11, I'm fairly confident it hasn't been "nightmarishly buggy" for everyone. (Neither of my two iOS devices, nor my roommate's two devices, nor my BFF's two devices, had any issues during upgrading, although I'm consistently finding an irritating-but-not-showstopping bug in bluetooth keyboard support on the iPad.)
More relevant to the parent, though: the upgrade to APFS happened in iOS 10.3, not iOS 11. So whatever bug you may have had with iOS 11 probably have nothing to do with the file system.
I'm not saying it's the be-all end-all of validation, but I don't see HN in there. As an Android user, it was not on my radar at all. This is the first I've heard. Sux2Bme, sure, but I think I'd have seen it somewhere.
More relevant to the parent, though: the upgrade to APFS happened in iOS 10.3, not iOS 11. So whatever bug you may have had with iOS 11 probably have nothing to do with the file system.