Single-day Weight spike after Apple Health backfill

torcator
torcator image
in Bug Reports

Hi team,

I’m seeing a persistent weight error on one specific day in my graph/diary (see attached screenshot). In Apple Health the entries are correct and continuous, but in Cronometer that date shows a spurious spike/outlier.

Environment

  • iPhone + Apple Watch
  • Apple Health integrated with Cronometer
  • Data type: HKQuantityTypeIdentifierBodyMass (lbs)
  • Time zone: local; no manual overrides

Steps to Reproduce

  1. Connect Apple Health to Cronometer.
  2. Ensure normal daily Body Mass samples exist in Health for the period.
  3. Open Discover → Weight Change (or diary) in Cronometer.
  4. Observe a single-day value that does not match Health.
  5. Run Settings → Integrations → Apple Health → Backfill → Weight and reopen the app.
  6. Issue persists.

Expected

The per-day Body Mass in Cronometer mirrors Apple Health (same value, timestamp bucket, and unit).

Actual

On 2025-08-31, Cronometer displays an incorrect weight (large spike). The value remains after backfill, app relaunch, and device reboot.

What I’ve Verified

  • Apple Health shows correct samples (no duplicates), correct Data Source priority (Apple Watch on top), correct units/timestamps.
  • Tried disconnect/reconnect + backfill; force-quit; Background App Refresh on; Low Power Mode off.

Questions

  • Does Cronometer apply rounding/averaging/dedup or a time-bucket rule that could pick the wrong sample when multiple exist on a day?
  • Is there a way to purge and re-import Body Mass for a single date only?
  • Any known issues with midnight boundaries, unit conversion (lb↔kg), or timezone offsets for HKQuantityTypeIdentifierBodyMass?
  • Do backfills fully honor Health → Data Sources priority?

Happy to provide exact timestamps/values, app build, and iOS/watchOS versions.

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