Out-of-order Event

An out-of-order event is one whose arrival order at the server does not match its true occurrence order; a later event arrives first and an earlier one arrives after.

Arriving out of order is a natural result of delay: an offline queue draining at once, batching, a network retry, or a wrong device clock all disturb the order. Why does it matter? Because part of analysis depends on sequence, not just count: a funnel that cares about step order, path analysis, and any 'first this then that' logic gives a wrong result with a wrong order. The right way to handle it is to reconstruct order from the event timestamp rather than the arrival time, provided the timestamp is trustworthy. The common trap is a funnel showing a false drop because the second step's event was inserted before the first; before any conclusion you must ensure the analysis is ordered on event time, not insert time.