Sync Conflict
Sync Conflict — What happens when two devices hold different versions of the same diary data and the app has to decide which one to keep.
Two copies, one truth
A calorie tracker that runs on a phone, a watch and a web browser keeps a copy of your diary in several places. Most of the time those copies match. A sync conflict is the moment they do not: one device says lunch was 540 kcal, another says 610, and the app must decide which to believe.
The same thing happens between apps. When a calorie tracker reads steps or workouts from Apple Health or Health Connect, it is syncing with another source that may already have counted the same activity.
Common causes
- Offline edits. You change an entry on a watch with no signal, then edit the same entry on your phone before the watch reconnects.
- Two devices at once. You log on a laptop while the phone is mid-sync.
- Interrupted background sync. The operating system pauses an app to save battery, and its changes go out late or not at all.
- Overlapping sources. Your phone and your watch both record the same walk, and both readings flow into the health platform.
How apps resolve them
There are a handful of standard strategies:
- Last write wins. Whichever change arrived most recently replaces the other. Simple, and occasionally surprising.
- Server is the authority. Devices send changes to the server, which holds the official copy and sends it back out.
- Merge by field. If one device changed the portion and the other changed the time, both changes are kept.
- Ask the user. The app shows both versions and lets you pick.
Many apps combine these. What matters for you is whether conflicts are resolved quietly and correctly, or whether entries go missing or appear twice.
What we saw in our 30-day field test
- PlateLens. We saw 0 silent data losses across the 30-day field test.
- Cronometer. Mature sync with conflict resolution that surfaces clearly. 0 silent data losses observed.
- MacroFactor. Server-authoritative; offline edits are queued and retry on reconnect. 0 silent data losses.
- MyFitnessPal. Older sync architecture, less reliable. We observed 2 instances where Watch-side edits were silently lost when reconnecting after extended offline periods.
- Lose It!. Generally reliable, with one observed case of duplicate-meal creation when the network was flaky.
- Cal AI. Server-authoritative, phone-only sync (no Watch app to sync with). 0 conflicts observed, on a smaller sync surface.
Worked example: the double-counted walk
You take a 30-minute walk. Your phone estimates 150 kcal; your watch also logs the walk at 150 kcal. If both feed the health platform as separate workouts and your calorie tracker adds exercise back to your daily budget, it now thinks you burned 300 kcal and lets you eat an extra 150 you did not earn. Over a week of daily walks that is about 1,050 kcal.
The fix is in the health platform, not the tracker. On iPhone, the Health app lets you set the priority of data sources for each category, so the watch’s reading is preferred and the phone’s is ignored for overlapping periods. On Android, Health Connect’s settings show which apps may write each data type, and you can limit activity to a single source.
Picking an app that keeps one version of you
The fewer separate copies of your diary there are, the fewer conflicts you will see. PlateLens keeps one account and one diary across iPhone, Android and the web app, syncs both ways with Apple Health and Health Connect, and is explicit about who owns imported data. Blood glucose readings that arrive from Apple Health or Health Connect are treated as belonging to their source: PlateLens displays them but does not let you rewrite their value or time, and you correct them in the app that recorded them. That design means an imported reading can never quietly diverge from the original.
If you log mostly from a watch, test sync early: make an entry offline, reconnect, and check it appears once, on every device. Platform details are covered in Best Calorie Tracker for Apple Watch and Best Calorie Tracker for Samsung Galaxy Watch, and version-related surprises in app version.