Hang in there for a few more reviews. I had the same thing happen early on. It is frustrating that a single 4 star takes so very long to be re-balanced ... it took 5 more before I got back over 4.5! And it doesn't seem like old reviews ever fall off.
I had one stay where the heat failed and it was during a super cold snap. I did place a single- night refund to their stay that helped mitigate it a bit. But I don't do that unless something goes wrong for a very long period.
Someone else suggests reaching out directly to the Guest to ask for more background on why only 4 stars was chosen. Nerve wracking, I know but... there's not much you can do once it's in there. 😕