Afaik HN checks its cache for duplicates. This means if the cache is used up by something else (e.g. a long discussion about GDPR) the old submission gets flush

Afaik HN checks its cache for duplicates. This means if the cache is used up by something else (e.g. a long discussion about GDPR) the old submission gets flushed out quite early and a duplicate submission after only a short time is possible.