In a treble bet, if one selection is lost, does it mean that the whole ticket is lost?

Why is the status set to pending lost? Will the result be different if the other 2 selections are voided, won or lost?

There is a possibility that the selection result changes (to won or voided), either due to some mistake or a change in the game conditions. That is why the ticket is not finally settled until all the selections are resulted and confirmed.