Why Both Dates Are Often the Same
First seen and last seen landing on the same day is the normal case rather than a fault. It means we have seen you exactly once, so the moment we found out you exist is also the most recent thing we know about you.
What Moves It
A server that reports to us seeing you again. When one does, last seen moves to that sighting and your name and skin are refreshed along with it.
Playing somewhere that does not report to us moves nothing, however long you play. Most servers do not report, so most profiles sit still.
This is not a record of your play time and we could not build one if we wanted to. We only ever know about the moments something told us about.
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