Missing or stale data
The three-step check before anything else.
Step 1 - check freshness
Settings, your connection card: find the dataset that looks wrong. If its last sync is recent and OK, the data is not stale - the difference is probably a definition, see Why numbers differ from Seller Central.
Step 2 - check the backfill
If the missing data is old history (last year's sales, June's sessions), look at the backfill percentage. Below 100 means it is still filling - deep history arrives over days, oldest last. This is normal for weeks after connecting.
Step 3 - check the window you are viewing
Ads reports reach back about 65 days (Amazon's limit). Sessions backfill one day per day. Settlement-based fees exist only where settlements have posted. If the view's window reaches past the data's natural floor, the gap is Amazon's retention, not a sync failure.
Still wrong?
If a dataset shows repeated sync errors, or fresh data that should exist simply is not there, use Feedback & Support in the app and mention the dataset name - the report reaches us with your sync history attached, and we can see exactly what Amazon returned.