@SagaiArt: Probably almost everyone on this forum can sympathize with you but there are innumerable threads on this forum about your exact issue. As it says right on your Star Seller page, you need to reply to the FIRST message of a NEW THREAD. It does not matter who sent it, the subject matter, if it is a duplicate or blank or anything else. If it is SPAM then it should be marked as such. Those have always been the rules.
Etsy is now putting a blue text warning / advisory (blue banner on desktop, and a blue dot on mobile) on those messages they consider to be a "new message" but should semantically be called a "new thread".
Subsequent messages from the same account (a buyer may have multiple accounts) are supposed to be combined into a single thread - with some exceptions.
Help Requests always start a new thread.
If you are creating a custom listing based on a new thread, you still need to reply to the message.
Cancellation requests in a new thread must be replied to in the actual message - replies using the cancellation form do not count as a response.
If the unanswered message is not a Help Request, at least for the time being, it appears that marking an unanswered message as SPAM (even after the 24 hour deadline has passed) will cause your reply percentage to change in a day or two if the original message was within the current star seller period (but not retroactively). Note that subsequent messages from that account may go directly to the SPAM folder.
