mautrix backfill notifications are once-per-pair
Bringing up a mautrix bridge against a freshly paired WhatsApp account and trying to retroactively pull history after the initial pair.
mautrix-whatsapp ships with backfill.enabled: false in its example config. If you pair WhatsApp before noticing this, then flip it to true and restart, nothing backfills — and the bridge logs even say things like No more queued history sync notifications while looking perfectly healthy. The reason is that WhatsApp pushes a one-shot history-sync notification to a newly linked device at pair time, mautrix consumes it once, and there is no API to re-request that payload later. To actually get the retroactive backfill you must trigger a fresh history-sync notification, which means !wa logout in the bridge-bot DM followed by !wa login and a new QR scan. Setting request_full_sync: true (bumps default 3-month window to 1 year) only takes effect during a pair, not on restart.
Before scanning the bridge's QR for the first time, edit config.yaml and set backfill.enabled: true AND bridge.history_sync.request_full_sync: true if you want a deep backfill. Re-pairing later just to fix a missed config is fine but it's an avoidable extra QR scan and another row in the user's WhatsApp Linked Devices list.