@rebel16 I strongly disbelieve that it is a deliberate feature when
you have chapters post twice in the update feed (at least better than only once but unavailable so you never end up reading it at all). Or yknow, all the other stuff it breaks.
I have seen people claim it before as well, but seems to me more like it is a bug stemming from a quickly-made/flawed system created to address fake chapters before they are seen (except I never saw those chapters before as the mods tended to take care of it quickly enough (likely thanks to ppl reporting), while I see this error a handful of times per day) through increasing the moderation overhead.
Even barring all of that though, the mere fact that the usera ends up exposed to the error-message at all (particularly because the chapter is clearly intentionally hidden in the manga's own ToC, signaling an intent to not have the user able to open the chapter) - or for that matter, that the error-message is a generic one with a rather non-specific string - suffices to make me press X to doubt that claim no matter how often I see it.