React Native field app with offline sync and conflict resolution

A facilities management company, 180 inspectors across manufacturing sites with patchy 4G, replaced paper checklists with a React Native app. Prior vendor build lost data when uploads failed silently.

Requirements: offline form capture with photos up to 25MB; digital signatures; supervisor approval; ERP export by end of day; MDM deployment on corporate Android fleet.

Architecture: Expo prebuild with custom native modules; WatermelonDB for offline storage; background fetch upload queue with exponential backoff; presigned S3 URLs; Node API with idempotency keys on submission IDs.

Problems faced: Android Doze killed background sync until whitelisted; iOS photo HEIC conversion inflated server storage, client-side JPEG cap added; conflict when supervisor edited same checklist online while inspector offline, last-write-wins with audit diff surfaced in admin UI.

Release: staged rollout via Play Console internal track; Crashlytics + Sentry; OTA updates for JS-only fixes.

Outcome: 99.2% submissions synced within 24 hours; paper process eliminated at four pilot plants; expansion to full fleet over three months. Client anonymized, facilities management operator.