why client_upload_time is earlier than client_event_time?

Question

I see in some of the events that client_upload_time was long before client_event_time. How can upload  event happen before the event was generated? Here is one example record.

Beth Saunders · Accepted Answer

Hey @Kevin Zhang, thanks for the example. The device clock was set ahead when the event was recorded, so the event’s client_event_time is in 2025, while the upload and server times are in 2023. Because the client and server upload times matched closely, Amplitude kept the device’s event time as the canonical event_time. This can make it look like the upload happened “before” the event. The fix is to ensure device clocks (or any custom timestamp logic) are correct; for audit/order-of-arrival views, rely on server-side timestamps which aren’t affected by device clocks. (“client event time shows unexpected value”)