the installer log said all went well... so how can we tell where it failed?
You can't. And not even the updater itself can say for sure, in *every* possible situation.
The issue is, for obvious performance reasons, the updater is not checking all files, one by one, online, against your local copy. It first downloads an index that contains the list of all files in the server with their individual checksum, and then it compares them locally from the list, to know what is outdated.
This is very fast, and always works unless...in addition to the actual file being outdated, even the LIST ITSELF is outdated so, from the point of view of the updater, everything is fine.
This is of course very rare, but can possibly happen, because after an update, it takes a bit for all the network of Cloudflare servers ( there are 190+ in the whole world ) to get the latest updates. It usually takes only an hour or so, but sometimes, in some countries, it might take longer.
Of course, we couldn't possibly use a single server for the Live Update, the users are just too many, and a single server would never be able to cope with the load of everybody downloading an update at the same time, so we must use a global caching system, which has the side effect of not everybody getting the latest files at the same time.
