One home landed a week late for someone in Sundsvall. The cause was two seconds, and the only way to find it was to look at what actually happened.
Collection of new listings starts on the hour, every hour. The weekly email went out on the hour too. Two jobs starting in the same second sounds harmless until you look closer.
The send was reading from the database while collection was still writing to it. A home that landed on the wrong side of that boundary missed the week's email and waited for the next one. For a weekly email, that's seven days.
Nothing was lost, but a week is the entire product for someone on a weekly cadence. The send moved to 09:15, and the rule since then is that no job which reads listings may sit on the hour.
