If you thoroughly checked your Notifications/Inbox combo (easy to miss something because sometimes you have 2 “conversation threads” (order page + “normal” inbox) with the same person because of that twofold message box!) and are sure there aren’t any messages, including spam messages, you missed, you probably should contact support and ask them about it - as obviously it should not affect your analytics as a seller if you don’t reply to those BR offers which you can not reply to.
Are you sure that not one of the sellers who sent you offers for your BR didn’t also contact you through your contact me button? Just asking as they could do that, or even sellers who see your BR could contact you without sending an actual offer, since, unlike if you were “only” a buyer, they can look up your name and contact you without sending an offer, or in addition to sending you an offer, and them contacting you outside of sending an offer to the BR, of course would need you to reply to keep your rate up.
Hope I didn’t make it sound as complicated as it is.
I wouldn’t completely rule out it affecting your analytics even if you’re 100% sure you checked everything else and didn’t miss to reply to any “normal” messages, I recently had my response rate drop by a whopping 5% because I didn’t reply to a spam message by a seller I had a transaction with, and which as far as I was concerned, was over, since I had communicated, completed and rated and all and was the buyer in that transaction, but it still counted, obviously.
So, I’d say, check your Notifications/Inbox once more to make sure there’s nothing you missed, and if there’s not, contact support.