@Maia29 If you failed to either accept or decline a booking request within the 24 hours, even if you messaged the guest back, that would lower your response rate. Is it possible that that happened at some point?
I know I went from 100% to 98% a couple years ago because Airbnb stopped sending me my text notifications- I missed a request, and even though I messaged the guest back in 25 hours, apologizing and explaining what had happened and she still went on to book, Airbnb dropped my response rate. Pointing out to them that it only happened because of their notification glitch did no good, surprise, surprise.
In any case, 98% is still well above the threshhold, so I wouldn't concern myself with it.