I don't understand why my score keep going down despite that i am anwering all emails within 24h. Would u please help ?
You have to reply to Etsy messages from your shop dashboard, not emails.
It went down today because the review period changed and an entire month of messages has dropped off.
@MineralsParis: eMails do not count, only Etsy messages (aka Convos). Check the applicable CSV file from your Star Seller page to see which messages Etsy thinks you answered late. Remember that the stats you now see are for the January star (October, November and December). The "Last Review Period" shows the stats for the December Star (September, October and November).