The author reports that he experienced a failure of the app prior to noting the issue (and implies that it may have been due to an improper shutdown). It's a reasonable hypothesis that this failure corrupted the local cache in a way that note from being synced. Note that creating a new note with the same content resolved the issue, supporting the hypothesis that the note in question was corrupted in some way. So this is not a general transparent failure of the application, but a specific (and apparently minor) fault that appears to have been the result of an obvious event. If your tv stops working after it falls over, that's not an indication of a general problem for that model of tv in cases where they haven't fallen.
Author reports that changes prior to app failure weren't synced (that is, the note isn't present at all in the web version). That either implies the sync functionality had failed long before this event (and worse, failed in a manner not apparent to the user) and that corrupting a local copy of a file somehow wipes out the synced cloud copy (which largely defeats the purpose of sync as a backup method).
This isn't a general failure of the application but it does indicate that the sync code is not robust and could result in data loss that, from the user's perspective, is catastrophic.
