Your rating will change on a day when nothing happens.
Etsy's shop rating counts only the last twelve months. So it moves twice for every review: once when the review arrives, and once when it turns a year old and stops counting. Etsy emails you about the first. Nobody tells you about the second — and that one you can see coming.
4.72
shows as 4.7
no change since the last check
KilnAndClay
39 reviews in the last twelve months
3.54.5
4.74.8
4.95.0
On 16 Aug (17 days) a 2-star review turns a year old and stops counting. Your figure would rise from 4.7 to 4.8.
3 more five-star reviews would put you above 4.8.
Two ways to get to 4.8, and one of them is a date rather than work. That is the whole idea.
Sign-in reads your email address and nothing else. Your Etsy account is never connected — a shop's rating is public, and public is all this needs.